Necessary for a portfolio?

Question: Receiving orders for work from clients and assign them to freelancers. But, I am not from IT business but administration.
Comment: Hi Omaruko, welcome to Freelancing.SE! I am having a hard time understanding what your question is that you are asking. Can you [edit] to clearly mark a *question* you need answered? For more information, please refer to [ask]. Thanks!
Answer: As admin, it is unlikely that you will have a portfolio. Instead, you should create a solid CV and present this when asked for details about previous work.
In addition, speak to your current/previous employers and ask if they would be happy to write you a reference, or a recommendation on linkedin.
Comment: Thank you for reaching me out.
The reason why I have asked you for the following reason.

1.I would not make a permanent contract prospective clients.
  Therefore, the portfolio is preferable than CV, I think.
2.Here is the example of the portfolio , which is the person who has not related the web, or rather he/she is an admin.

Awaiting for your further comments or suggestions.
Comment: Sorry, I forgot to put the URL.
https://workshift-sol.com/users/view/15354
Answer: A portfolio can give you an idea of the quality and style of a freelance designer. witch can be a helpful tool to made decisions (witch work, witch frelancer).  But if you don't have a background or experience in design it will be pretty useless.
I never find much use in a portfolio from a developer/programer because a portfolio is more visual and development have many relevant background aspects that a portfolio can show.
Comment: Thank you for reaching me out.
Please refer to my comment as I have replied for Mr. John HC.
Answer: If you can get reference letters from previous customers/clients I would add to your portfolio page  words such as
" On specific request, if required during negotiations, we can present letters of recommendation from past and present clients."
PS what is "&amp" mistype in the English text.
Comment: I doubt why reference letters have anything to do with my question.Your reply is off the point.

Necessary for a portfolio?


Is it okay to keep track of accounts receivable and accounts payable with cash basis accounting?

Question: Is it okay to keep track of accounts receivable and accounts payable for my reference but still mark cash basis accounting on my tax return?
Answer: Yes
The IRS doesn't care what management accounting system you use for your personal use, only that you use the system they prescribe when talking to them.
If you look at the accounts of any public corporation they will almost always show figures for future tax liabilities and/or assets. That's because the accounting system they are required to use in their annual report doesn't line up with how they report and pay their taxes.
Comment: Thank you! If I was audited, and had marked cash basis on my tax return but all of my records had accounts receivable and accounts payable, would there be a problem?
Comment: @Someone modern accounting software can produce both types of report.
Comment: What if my software can't? I don't think `ledger` (https://www.ledger-cli.org/) can. Do I need to switch to another accounting program?


What does aspect ratio mean in memory?

Question: Does anyone know what aspect ratio mean in memories? and how it's different in block ram and distributed ram in Xilinx FPGA?
Thanks
Answer: "Aspect ratio" refers to the number of address bits and data bits when accessing memory.
For example, say you have memory that holds 65,536 bits. If you use 8 data bits per address, you have 8,192 addresses (65,536 / 8 = 8,192), which means 13 address bits (2^13 = 8,192). So one aspect ratio for accessing 65,536 bits is 8 data bits and 13 address bits.
But say you want 16 data bits per address. Then you can only have 4,096 addresses since 4,096 * 16 is 65,536, and that's all the memory you have. In that case, you can only have 12 address bits. So another aspect ratio for accessing 65,536 bits of memory is 16 data bits and 12 address bits.
Answer: Aspect Ratio is another term that is used for the data organization of a RAM block.
In Xilinx FPGAs, a Block RAM is a dedicated two-port memory containing several kilobits of RAM. The FPGA contains several (or many) of these blocks.
Inside of each small logic block is a configurable lookup table. It is normally used for logic functions, but you can reconfigure it as a few bits of RAM. You can combine several (or many) of them into a larger RAM. This is distributed RAM.
Both types of RAM can be initialized with data, or used as ROM.
More Information can be found here:
http://www.xilinx.com/support/index.htm#nav=sd-nav-link-182711&tab=tab-sd

What does aspect ratio mean in memory?


How could a statement be true without proof?

Question: Godel`s incompleteness theorem states that there may exist true statements which have no proofs in a formal system of particular axioms. Here I have two questions;
1) How can we say that a statement is true without a proof?
2) What has the self reference to do with this? Godel sentence "G" can say that SUB(a,a, no prove) but could be this just arbitrarily judgement about non-provability of "a" because it may simply has a proof which is not yet revealed or discovered?
Comment: For (1), a thing that actually happens is this: you may have a predicate $\mathfrak S$ of natural numbers such that, for any fixed $n$, $\mathfrak S(n)$ can be verified in a finite number of steps. However, it turns out you cannot prove using the axioms at your disposal whether $[\forall n,\mathfrak S(n)]$ is true or not. In such a case, $[\forall n,\mathfrak S(n)]$ **must** be "true", in the sense that, whenever it is actually provable, it is true.
Comment: "True" is a property of the actual natural numbers.  "Provable" is something about a particular system of axioms that try to describe the natural numbers.  Adding more axioms may make more things provable.
Comment: @G.Sassatelli: What you say is correct, though indeed it's not the full picture. The phenomenon you describe is called $ω$-incompleteness. PA is $ω$-incomplete for the following interesting reason. PA decides (proves or disproves) every quantifier-free sentence over PA. Con(PA) is an independent $Π_1$-sentence over PA (Essentially saying that every string $x$ is not a proof of "$\bot$"), but each of its instantiations is provable since PA can verify each step of a proof. We more precisely say that PA is not $Π_1$-complete. But note that PA is $Σ_1$-complete.
Comment: @G.Sassatelli: Sorry I made an accidental mistake in my last comment, so I've deleted it. Here is the corrected version. Every structure $M$ over the language of PA that satisfies "$φ(k)$" for every $k \in M$ must also satisfy $\forall n\ ( φ(n) )$. The sentence Con(PA) shows that it is possible that $\def\nn{\mathbb{N}}$$\nn$ satisfies "$φ(k)$", and in fact PA proves "$φ(\underbrace{1+\cdots+1}_\text{$k$ terms})$", for every $k \in \nn$, but that PA does not prove "$\forall n\ ( φ(n) )$".
Comment: (that's as much as I know on the subject, though :) )
Comment: @G.Sassatelli, even if it's not the full picture, you still made this very clear, so thank you. I was wondering about this too
Comment: Another interesting thought is proving un-provability.
Comment: The short answer is, you have 2 logics, the statement is true in one of the  logics but not true in the other logic.
Comment: @DanielV: your short answer is not a very good answer: the statement is provable in one logic but not in the other. Truth and provability need to be carefully distinguished.
Comment: @RobArthan I've never seen a coherent definition of truth distinct from provable that amounted to anything more than "provable in another logic", unless you are talking about "real world" truth (like physics).  I would like to see an example that distinguishes the concepts though.
Comment: @DanielV: I am not talking about anything as dubious as the physical world, but just about truth in the domain of natural number arithmetic. If you don't accept that as a given, then you can't coherently talk about language or logic.
Comment: @RobArthan: DanielV's comment is almost correct. The reason is that even the reasoning in the meta-logic is done in a formalizable system. We often use ZFC for example as the meta-system, and ZFC gives us this object which we call $\mathbb{N}$. But it could very well be that ZFC is inconsistent!!! What then? It means that whatever ZFC proves about provability in some formal system (like say PA) is useless. (We would then look for a new foundation that we hope is consistent and can prove consistency of PA.) Also, what if ZFC is consistent but Σ1-unsound? Then its idea of $\mathbb{N}$ is weird..
Comment: @DanielV: What's incorrect in your comment is that (arithmetical) truth is not at all defined in terms of provability, and cannot be. A sentence over PA for example is not even a meaningful sentence over ZFC, so it makes (almost) no sense to say that it is provable over ZFC. However, we can define what it means for a system $S$ to interpret arithmetic, which in short means that there is a (computable) translation from sentences over PA to sentences over $S$ that respects modus ponens such that $S$ can prove the (translated) axioms of PA but does not prove the translation of "$\bot$".
Comment: @DanielV: Then we can say that any (arithmetically) true sentence is indeed provable under translation in the meta-system. But that is quite useless; $Th(\mathbb{N})$ of course proves every (arithmetically) true sentence and its translation is proven by the meta-system! That is why we define (arithmetical) truth in terms of truth in the standard model, and not provability. However, a consistent meta-system that interprets PA will be unable to prove or disprove some translated arithmetical sentence by Godel, and hence cannot prove the (arithmetical) truth of some sentence over PA!
Comment: @SimpleArt: See http://math.stackexchange.com/a/1766631/21820 and http://math.stackexchange.com/q/1783680/21820.
Answer: Your confusing stems from the way many articles about Godel's incompleteness theorems are extremely imprecise. Here is a proper definition.
$\def\nn{\mathbb{N}}$

We say that a sentence $φ$ over a language $L$ is true in an $L$-structure $M$ iff $M \vDash φ$.
For convenience, when $L$ is the language of arithmetic, we say that $φ$ is true iff $\nn \vDash φ$.

Note that these definitions are only possible in a meta-system that already has a collection called $\nn$ (also known as the standard model of PA). Thus:
$\def\t#1{\text{#1}}$
$\def\con{\t{Con}}$
$\def\pa{\t{PA}}$

"$φ$ is true but unprovable" is more precisely "$\nn \vDash φ$ and $\pa \nvdash φ$".

Now there is a sentence over PA denoted by $\con(\pa)$ such that PA is consistent iff $\nn \vDash \con(\pa)$ (in other words PA is consistent iff $\con(\pa)$ is true in the standard model). It is in fact non-trivial to show that such a sentence exists, which is a crucial part of Godel's first incompleteness theorem.
The remainder of the incompleteness theorem shows that $\pa \nvdash \con(\pa)$. But the meta-system we choose always has $\nn \vDash \pa$, so $\pa$ is consistent and hence $\nn \vDash \con(\pa)$. Thus $\con(\pa)$ is the first natural example of a sentence that is true but unprovable (in the precise sense defined above).
Note that it is false that every true but unprovable sentence $φ$ can be proven by $\pa+\con(\pa)$. In particular, $\pa+\con(\pa) \nvdash \con(\pa+\con(\pa))$, even though $\nn \vDash \con(\pa+\con(\pa))$ (by essentially the same argument as above). This can be proven simply by applying Godel's proof of the incompleteness theorem to $\pa+\con(\pa)$.
Better still, we can let $\pa_0 = \pa$ and recursively let $\pa_{k+1} = \pa_k + \con(\pa_k)$ for every $k \in \nn$, and then let $\pa_ω = \bigcup_{k\in\nn} \pa_k$. Then we still have $\nn \vDash \pa_ω$, and yet $\pa_ω \nvdash \con(\pa_ω)$ even though $\pa_ω \vdash \con(\pa_k)$ for every $k \in \nn$.
Comment: Also see the links in http://math.stackexchange.com/a/1684208/21820 for introductory material to logic, as it is difficult to grasp the concepts here without a proper understanding of logic.
Answer:
Assuming your formal system is consistent, Gödel shows there is a statement in that system whose interpretation is true but that is unprovable in the system.  The statement is actually provable, but not in that system: you need the additional assumption that the system in consistent, and that is not provable in the system (unless the system happens to be inconsistent!).
There's no "arbitrarily judgement" here. If there were a proof of "a", you could use that to produce a proof of 0=1. Thus if the system is consistent, "a" is not provable in the system.
Comment: Unprovability is not the same as falsehood; the assumption that it is is the assumption of completeness itself. This is question-begging in the context of Gödel's proof.
Comment: What if "a" is false, then within the system, we prove that it is not provable which means it is true (because we can not prove that it is false which means it is true). This means that it is true and false at the same time even if the Godel`s sentence is true.
Comment: Sorry but your answer is wrong. Assuming the system is consistent does not have anything to do with (arithmetical) truth, which is always the notion concerned. See my answer for an explicit sentence that is true in $\mathbb{N}$ but not provable no matter how many times you add the assumption of consistency of the system to itself.
Comment: @user21820 That's incorrect. Robert Israel is not saying that consistency lets you prove everything - just that a consistency hypothesis is needed to prove *the specific example he mentions* (which is absolutely correct).
Comment: @NoahSchweber: It's a year since my comment, but on reading my own comment it seems that I had interpreted Robert's claim to be about any independent statement, rather than the Godel sentence specifically. Also, Godel's original proof required ω-consistency, not just consistency, so there are multiple places in his post that needs fixing or clarification.
Comment: @user21820 That's incorrect - Goedel's argument required $\omega$-consistency to show that the theory didn't **disprove** its Goedel sentence; you only need consistency to show that it doesn't **prove** its Goedel sentence. This answer is completely accurate. And I don't think "there is a statement in that system whose interpretation is true but that is unprovable in the system. The statement is actually provable, but not in that system: you need the additional assumption that the system in consistent" needs clarification, it's clear that "the statement" refers to the only statement mentioned.
Comment: @NoahSchweber: Sorry you're right about the ω-consistency part; I didn't think carefully enough. As for the other point, I understand why you think the claim is clear enough, but I still think it could have been much clearer. Also, looking at my original comment again it seems I also thought his post was not answering the question clearly enough because it was about truth and not provability. This appears to also be *Malice Vadrine*'s objection. Anyway is there some reason you suddenly bring up this comment after a year of inactivity?
Comment: @user21820 Sorry, I didn't realize this was a year old (I got here following related questions). I disagree with Malice Vadrine's objection but I guess that's subjective.
Comment: @NoahSchweber: Okay, anyway thanks for prompting clarification of my comments, for the sake of other readers. I agree it's subjective; I just like making the distinction clear because confusing the two is the source of nearly all misunderstandings about the incompleteness theorems.
Answer:
1) How can we say that a statement is true without a proof?

The main idea behind the standard definitions of truth used by most mathematicians and logicians that study mathematical logic, model theory and related topics is the one given by Tarski. As you can see at the link, he separated the concept of truth from the syntax of the language (for a good number of reasons, e.g., to not allow statements such as "this statement is false"), i.e., the truth concept is not given within the language but by the metalanguage. As the concept of proof is syntactical, at first you won't need any proved formula to be true or any true formula to be provable, but there's a property called soundness and it gives the following result:
In a first order theory, if $\Sigma \vdash \varphi$ then $\Sigma\vDash \varphi$.
First, $\Sigma \vdash \varphi$ means that a set of formulas $\Sigma$ can prove the formula $\varphi$, i.e., you have $\Sigma$ and logical axioms (and, maybe, some aditional nonlogical axioms from the theory) as assumptions and are able to derive or deduce $\varphi$ using the rules of inference of your theory, so this is a syntactical process. Now, in my notation, $\Sigma \vDash \varphi$ means that all structures (which carry the concept of truth) that satisfy the formulas in $\Sigma$ also satisfy $\varphi$, in other words, if all formulas in $\Sigma$ are true in some structure $\mathfrak{M}$, then $\varphi$ must be true in $\mathfrak{M}$. As $\Sigma$ usually is a set of axioms that define a theory, if $\mathfrak{M}$ is a structure that satisfies $\Sigma$ (i.e., all formulas in $\Sigma$ are true in $\mathfrak{M}$) we say that $\mathfrak{M}$ is a model of $\Sigma$. In his doctoral dissertation , Gödel proved the converse, which is known as his Completeness Theorem:
In a first order theory, if $\Sigma \vDash \varphi$ then $\Sigma\vdash \varphi$.
We say that a theory is complete in that sense (some authors call it semantically complete, to not make confusion with other type of completeness that is used in the Incompleteness Theorems, which they may call syntactical completeness) if this statement is valid (and it is, Gödel proved it).
Now we can observe the fact that in some theories there are statements that can't be proved as well as their negation, you don't need to go too far to have some examples of this happening, if you have a system where you axioms $\Sigma$ are the Field Axioms you can't prove the formula $\varphi$ where it is $(\exists x)(x^2=-1)$ for the following reason: we can see (in a not rigorous manner) both $\mathbb{C}$ and $\mathbb{R}$ as models of $\Sigma$ and $\varphi$ is true in $\mathbb{C}$ (as you can take $x=i$) and false in $\mathbb{R}$, which means that not all models of $\Sigma$ satisfy $\varphi$, i.e., $\Sigma \nvDash \varphi$ and, by the soundness property, we have that $\Sigma \nvdash \varphi$ and, with a similar argument, you also have that $\Sigma \nvdash \neg \varphi$.
Now that we know that there are some theories that have statements that you can't prove (as well as their negation), we call such systems incomplete (or, as I commented early, syntactically incomplete), what Gödel showed in his First Incompleteness Theorem was that any first order theory that satisfy some conditions will be incomplete, and that proved that, because the way mathematicians axiomatize the standard mathematical theories, we can't scape from the fact that there will always be statements such as $\varphi$ I showed early. In particular this will be valid for some theories that have a set of axioms $\Sigma$ with some properties and such that $\textbf{PA}\subset \Sigma$ where $\textbf{PA}$ is the set of Peano's Axioms.
On the other hand, mathematicians suppose that there's a standard model for arithmetics, i.e., a structure $\mathfrak{N}$ that satisfies $\textbf{PA}$ and every arithmetical statement, to be considered true, must be satisfied in that structure. Now I can finally give you an answer to your question: by the First Incompleteness Theorems, loosely speaking, any system of axioms $\Sigma$ (given some conditions) for the standard arithmetic will have statements $\varphi$ such that  $\Sigma \nvdash \varphi$ and  $\Sigma \nvdash \neg \varphi$, but $\mathfrak{N}$ satisfies $\varphi$ or $\neg \varphi$, that means that there will always be a true statement (a formula satisfied by $\mathfrak{N}$) that can't be proven by a given system of axioms $\Sigma$.

2) What has the self reference to do with this? Godel sentence "G"
  can say that SUB(a,a, no prove) but could be this just arbitrarily
  judgement about non-provability of "a" because it may simply has a
  proof which is not yet revealed or discovered?

The self-reference is just an argument used by Gödel in his original proof from which he was able to construct a sentence that is not provable by the system and will be true when you see it with the lens of the meta-theory. With all I said I hope you can comprehend that some statements in a given fixed theory are impossible to prove, it's not a matter of something not being revealed or discovered.
For further reference and lots of details and technicalities that are missing in my answer, as well as aspects of the problem consisting on deciding if a statement is true or not, I can recommend the following textbooks:

Hinman, Peter G. Fundamentals of Mathematical Logic. Wellesley, MA: A.K. Peters, 2005.
Dalen, Dirk. Logic and Structure. Fifith Edition. Berlin: Springer-Verlag, 2013
Tourlakis, George. Lectures in Logic and Set Theory. Vol. 1, Mathematical Logic (Cambridge Studies in Advanced Mathematics ; 82). N.p.: Cambridge UP, 2003.
Shoenfield, Joseph R. Mathematical Logic. Reading, MA: Addison-Wesley Pub., 1967.

There are also good references and links here and here.
Comment: So if the truth is isolated from the syntax of the proof of a particular statement within one theory, it should itself be a conclusion within another more general theory. Then what is the most fundamental true statement that we should begin in order to reach to the proof of any other possible statement? And more importantly, how could be know that this fundamental truth is true if it is not preceded with any other theory to prove it is true?
Comment: @Isaacadel Truth it's not a conclusion in a more general theory, truth is just a property that a sentence may have if there's model satisfying it. Inside a theory, a statement can be true or false depending on two things: if it's provable, then it's true (soundness), if its negation is provable, then it's false, if it's neither provable nor disprovable, it can be either true or false depending on your context (i.e., dpeneding on your especific model), think about my example. The question about fundamental truths is more philosofical than technical, you should ask it somewhere else.
Answer: As is convenient in discussions of the completeness theorems, let's focus on the theory of arithmetic over the natural numbers. We have a well-defined notion of truth in the natural numbers under the usual arithmetic operations: e.g., the sentence $\forall i\cdot \exists a, b, c\cdot \ a > i \land a^2 + b^2 = c^2$ asserts the existence of arbitrarily large Pythagorean triples and we "know" what that means (specifically it means that it is valid in what model theorists call the structure comprising the natural numbers and the usual arithmetic operations).
Now let's think about methods for deducing which sentences are true in this theory, e.g., we might take our method to be first-order logic and Peano's axioms. What  Gödel's incompleteness theorem says is that (under some very reasonable hypotheses on the method), there is no method that will let us deduce all true sentences and no false sentences. The theorem does not say "there is no proof", it says "a specific method of finding proofs will never find one".
The philosophical interest is that the theorem applies to an enormous range of "specific methods of finding proofs" and indicates that there is no chance of finding an adequate foundation system for mathematics that can prove its own consistency.
Comment: While your explanation is not wrong, it is not the one that logicians have in mind for (arithmetical) truth (which I've defined in my answer). One could hence argue that Godel's incompleteness theorems have much less philosophical impact than Tarski's undefinability theorem, though both are essentially the same from a purely mathematical viewpoint (because mathematics is always done in a formal system). Hence I suggest that you clearly specify that "true" and "false" is in mathematics ill-defined without reference to a structure, because it's wishy-washy to say "we know what that means".
Comment: It's contentious from a philosophical point of view, that's true. But most modern logicians consider it to be so, and even go further than me by always asserting that the meta-system is ZFC. I don't even assume the meta-system to be ZFC, but I insist that one makes clear what is used, because otherwise **everything** one says is wishy-washy, and often people who refuse to specify their meta-system shift goal-posts. I don't agree with people who claim that mathematics can be done outside a formal system; their 'mathematics' is nothing but philosophical opinion (even if not necessarily false).
Comment: For a more precise calibration of possible meta-systems, see my (very) brief outline at http://math.stackexchange.com/a/1808558/21820.
Comment: Well you said "we have a well-defined notion of truth in the natural numbers" and later "we 'know' what that means". Read ordinarily, this means that you are relying on the intuitive notion of natural numbers as a platonic collection, but the fact is that we do not actually have a way to pin down any such thing. Natural language is problematic (see http://math.stackexchange.com/a/1867336/21820), so we need some formalizable meta-system. Modern logicians use ZFC, in which ω is a model of PA given by the axiom of infinity, and then define arithmetical truth based on whether ω satisfies it.
Comment: This notion is now implied by your updated answer. Note that it may well be the case that ZF is consistent and yet proves "not Con(ZF)", in which case ZF proves that ω does not satisfy "Con(ZF)", and yet if we move out one more level to a higher meta-system MS we can see that the natural numbers in MS do satisfy "Con(ZF)"! If it is difficult for you to grasp this, first consider the analogous situation of T = PA + not Con(PA), in which case you can check that T is consistent but proves "not Con(T)".


Is Torah considered Din el Batel (دين البطل)?

Question: Is Torah (sharia'a of Jew) considered Din el Batel (دين البطل)?
Comment: Idk what دين البطل means. But, anything other than Islam is wrong. And we would not say the Torah is wrong because we say proper understanding of the true Torah entails following Islam.
Comment: As Salaamu 3laykum, please see my answer below regardless of the votes.
Answer: دين الباطل means a false or wrong religion.
The Torah is a divine scripture, and can not be called a false religion, rather the Quran says about it:

إنا أنزلنا التوراة فيها هدى ونور يحكم بها النبيون الذين أسلموا للذين هادوا والربانيون والأحبار بما استحفظوا من كتاب الله وكانوا عليه شهداء
Indeed, We sent down the Torah, in which was guidance and light. The prophets who submitted [to Allah] judged by it for the Jews, as did the rabbis and scholars by that with which they were entrusted of the Scripture of Allah, and they were witnesses thereto.
— Quran 5:44

ولقد آتينا موسى الكتاب من بعد ما أهلكنا القرون الأولى بصائر للناس وهدى ورحمة لعلهم يتذكرون
And We gave Moses the Scripture, after We had destroyed the former generations, as enlightenment for the people and guidance and mercy that they might be reminded.
— Quran 28:43

The only issue with the Torah is that the people have distorted its interpretation and text.
Judaism (the creed and shariah of the Jews of our times) is a false religion. That is because it denies the prophets such as Jesus عليه السلام and Muhammad ﷺ, and it denies the Quran. And it has many other false beliefs and innovations. Nothing is acceptable from anyone now except to follow the religion of Islam:

ومن يبتغ غير الإسلام دينا فلن يقبل منه وهو في الآخرة من الخاسرين
And whoever desires other than Islam as religion - never will it be accepted from him, and he, in the Hereafter, will be among the losers.
— Quran 3:85

لا يسمع بي أحد من هذه الأمة يهودي ولا نصراني ثم لم يؤمن بالذي أرسلت به إلا كان من أصحاب النار
Whoever amongst the community of Jews or Christians hears about me, but does not affirm his belief in that with which I have been sent and dies in this state, he shall be but one of the denizens of Hell-Fire.
— Sahih Muslim
Answer: I'd like to add the following rather short remarks to the existing posts (as they already include some details).

دين البَطَل

Doesn't make any sense in Arabic as it literally means:

religion the hero or the hero religion

What you are meaning to say is either:

دين باطِلٌ

meaning a "wrong, false,void... religion" or:

الدين الباطِلٌ

meaning "the wrong, false, void ... religion".
or and this is less used, as it doesn't fit well:

دين بُطْل or
الدين البُطْل

which could be interpreted as "(the) religion of lies".

The Torah is one of the revelations of Allah so it can't be a leading to a wrong religion, even if -we as Muslims- believe that the original version was distorted (or at least it meaning/interpretation was distorted).
For this reason saying the "Torah is a wrong religion" is not appropriate.
The Torah similarly to the qur'an is a source of the Jewish shar'ia or Allah's shari'a in the original form, understanding and interpretation as it was taught by Allah's messengers() and prophets() who were sent to bani Israel (not exclusively).
From Muslim perspective both Judaism and Christianity became void by the revelation of the qur'an as both are asked therein to follow it, and similarly in their own revelation, they are asked to follow a messenger (often referred to as the Messiahs). Nevertheless some scholars say that whatever the qur'an has made void, by its revelation is void, but what is not remains applicable by Muslims. This view would for example support the fact of punishment of adulterers by stoning.
Therefore it is safer to say: Christianity and Judaism are void religions.
Answer: Bismillah Hir Rahmaan Nir Raheem
Hello,
I hope you are doing well. Thank you for asking your question. I am assuming you meant to say religion of falsehood. However, the Torah in its original form is one of the holy books. It came to Prophet Moses (peace be upon him). Then later Prophet Jesus (peace be upon him) was sent to have the people come back to the straight path. However, the jews did not believe in him and the group that did, altered his status and went against his original teachings.

Then the factions differed [concerning Jesus] from among them, so woe to those who disbelieved - from the scene of a tremendous Day. (Quraan chapter 19 verse 37)

And [for] their saying, "Indeed, we have killed the Messiah, Jesus the son of Mary, the messenger of Allah." And they did not kill him, nor did they crucify him; but [another] was made to resemble him to them. And indeed, those who differ over it are in doubt about it. They have no knowledge of it except the following of assumption. And they did not kill him, for certain. (Quraan chapter 4 verse 157)

And there is none from the People of the Scripture but that he will surely believe in him [i.e., Jesus] before his death.1 And on the Day of Resurrection he will be against them a witness. (Quraan chapter 4 verse 159)

When the Quraan came it came as truth to differentiate and clear the matter what the people had distorted. It gave respect to the Prophets (peace be upon them all), gave instructions as to the purpose of life and much more.
At the end of the day the Quraan says

Abraham was neither a Jew nor a Christian, but he was one inclining toward truth, a Muslim [submitting to Allah]. And he was not of the polytheists. (Quraan chapter 3 verse 67)

Conclusion
Any prior teachings were overwritten when the Quraan came. It gives instructions on how to live your life, describes past events that had occurred, differentiates right and wrong, etc.

Have a Nice Day!
Comment: @Ahmed, As Salaamu 3laykum, jazakaALLAH khairan for that clarification. I will revise that sentence.
Comment: "However when Prophet Jesus (peace be upon him) came then the clear differentiations began." ... This statement is factually incorrect. The Jews had gone astray way before the time of Prophet Jesus (Isa) and Prophet John (Yahya) .. They had committed many sins and killed a number of Prophets in the period between Moses & Jesus. The Quran speaks on this on several occasions.


Advice for an 18 year old about Investing?

Question: I'm currently 18, I already have investments in a variety of conservative mutual funds through the Stash app, however I want to get into actually investing for extra income. I currently have a steady cashflow along with expenses settled. Any advice helps! I have Robinhood downloaded but haven't really tried it yet.
Comment: By "actually investing", do you mean "picking individual stocks"?  And how conservative are your existing mutual funds?
Comment: @RonJon Yes, I want to start investing in actual stocks to get more experience. My current ETFs/Mutual funds are as conservative as it gets seeing as I just started this with the intentions of building a better life for the future. But now I'm trying to see (while also, still trying to build a better future) if I can make a little extra money off higher risk greater rewards I dont want to jump in head first though.
Comment: Mutual funds IS investing. One of the lessons I've learned over investing for almost 30 years is that individual stocks are usually a bad idea for investors for numerous reasons.
Answer: I'd highly recommend reading JL Collin's Stock Series. This is a great resource to teach you about how investing works, and gives you a primer on index funds, stock and bonds. Aditionally (and most importantly) it teaches you how to think about your money so that you don't make the bad decisions that so many people do by panic selling every time the market takes a dip. In general he recommends:

Pay off any debts you have.
Educate yourself so you're making the right decision. No one will care about your money as much as you do so make sure you understand what the best approach is for you.
Invest in total US (or world) market index funds (these are some of the safest long-term investments, that have been shown to consistently out-perform actively managed funds (over the long-term). They have historically averaged 10% returns, which is hard to beat without incurring a lot of extra risk. Use a broker like Vanguard which offers a low management expense ratio (MER).
Answer:
Do some reading - there's a lot of books out there
Find your leaning - equities (long term, day trading and everything in the middle), real estate (rental, flip), small business etc... determine what matches your personality profile, some of the above, all of the above etc. Each investment vehicle has its own set of positives and negatives.
Do it. Take action.
You will make mistakes, learn from it


Auto redirect Explanation

Question: I'm configuring a paypal payment gateway in my website, at the moment a sandbox is configured and I'm using paypal standard. Everithing works fine except for some small thing I need to discuss with you:

after user (redirected to paypal site) make the payment is there a way to redirect automatically after the payment is done...I would avoid that user has to click the link: "return to xxx website". ( I have seen and used many websites that use to redirect to paypal but after payments is done the really automatically redirect to the website...without any additional click)
I have personalized the aspect of my page under paypal account (in sandbox mode) but when i test the payment the page is not personalized but show the standard one...so my question is personalized pages works under sandbox?
For paypal standard subscribe button is required an HTTPS protocol or they accept also normal urls?
Answer: 1) If you are using PayPal Payments Standard (Buttons) then you will have the return to merchant at the checkout page, this is because the payment is complete at this point. What you are thinking when you are redirected back immediately is ExpressCheckout and the merchant can process the payment immediately or by user action.
2) Yes, personalized pages work in sandbox. You need to make sure it is set as primary
3) For PayPal Payments Standard you do not need HTTPS, as the payment is handled on the Paypal website.

Auto redirect Explanation


Why the AES perform encryption in 10 rounds Instead of one?

Question: I'm a Master's Degree student and researching about AES-128 encryption.
My Advisor asked me a question about necessity of iterative rounds in AES.
he asked:"why we couldn't encrypt a 128-bit plaintext with a 128-bit key by doing simple XOR operation on it? it have 2^128 key space and hard to attack.Why we should perform iterative rounds?"
can anyone explain it for me by references?
Comment: Block ciphers are meant to encrypt very long plaintexts, not just 128 bits.
Comment: So when the round key is inserted into the state what operation is used?
Comment: @Q-Club Carryless addition modulo 2, of course!
Answer: This is actually two questions, so its interesting that your advisor questioned it in this way.
The simple 128-bit XOR operation is what is known as a One Time Use Pad.  The cryptographic behavior of this is very well understood.  Some of its behaviors are desirable, some are not.  For example, they suffer from malleability if the attacker already knows the plaintext.
The question of why we use multiple rounds instead of one big round is a very different one.  We use multiple rounds because the construction of cyphers from small repeated rounds is well understood.  The security of it is easier to analyze.  For example, we can construct them in a way such that, in the event of an attack, there's a good chance that increasing the number of rounds solves the attack.  If we had one big algorithm, the probability that one failure may destroy the entire algorithm seems to go up.  I say seems to, because you can't prove such things with statistics, but the cryptographic community has found that, in general, its a rule that works.
Comment: On the first question, a reason _"why we couldn't encrypt a 128-bit plaintext with a 128-bit key by doing simple XOR operation on it"_ is that the key could trivially be found form a single plaintext/ciphertext pair, then allowing to perform any other encryption/decryption, against the security model of the block cipher. Nice explanation for the second.
Answer: Cort Ammon makes good points.  There is also another reason that rounds are required, to do with resources.
AES is essentially a substitution /permutation network with a block width of 128 bits.  It's technically impossible to make direct like for like substitutions of a 128 bit variable. You'd need ~10^40 bytes of RAM (2^128*16) to hold  a look up table. So AES does it in the SubBytes component using 8 bits at a time. To make this effective with the old confusion and diffusion adage, these substituted bits need to be permuted over the whole block width and the other 15 bytes.  That's what ShiftRows and MixColumns does.  But it takes more than one iteration.
If you look at the The Design of Rijndael, section  3.5, the bits can be fully diffused with just 2 rounds.  These two iterations effectively create a 128 bit wide S box.  The other 8 - 12 rounds add resistance to analysis.
Answer: Have only one big algorithm to encrypt is not considered a good design criteria
Encryption algorithms (ciphers) are constructed from building blocks like SBox, PBox , Rounds , Key schedule or expansion
Historically, one time pad algorithm which is a  simple Xor of plaintext with secret key usually chose random
The problem with this algorithm , if cipher-text got change in transit, the receiver has no way to detect such modifications
Compare the case, where we used AES for example to encrypt the plaintext, if change in transit , it will be decrypted to random message that could not be parse or recognized by receiver
Also, the cipher with iterative rounds , can be further enhanced by increasing number of rounds in case and attack is found
Also, the iterative round cipher could encrypt several blocks of 128-bit using the same 128-bit key whereas in Simple Xor cipher you could not do that and you will need as much secret key as plaintext nneded to be encrypted


How can I enforce that a user is only logged in once in Jboss/J2EE?

Question: I need to enforce that some users (that have a flag at true) can only have 1 active session.
I mean, the users logs in 1 browser and can't login in another browser/computer.
I tried using my own loginmodule but the second time I login (in another browser) the loginmodule isn't used, it seems something is being cached...
Answer: If you use Spring Security, there is an option for concurrent session control. You would want only 1 session. There is an explanation of integrating Spring Security with JBoss.
Comment: You can use Spring Security (previously known as Acegi Security) without using Spring.
Answer: You just need an Application Scoped map of logged in users that you check when someone logs in. Store the session id and the user id.
Are you using a Framework? If so which one?


Node Editor, Unwrapping, and FBX export not working

Question: I am new to Blender and Unity, so if you need me to add more information I can, any help is greatly appreciated. This all started when I tried to export my Blender object into Unity. So I had my object all created with materials and everything, it was unwrapped and UV projected, but when I exported it to unity as a FBX file the Materials didn't show up. I thought that was weird so I went back into blender and all my materials where gone I tried reapplying the materials and I couldn't. Now I can't seem to add materials, unwrap, add nodes, or UV project anything.

Blender File Link
Comment: If you can, also add your .blend file to the question. It helps us finding a possible solution.
Comment: Okay I added the link let me know if it works. Thanks for the feedback Ben
Comment: Works fine, I'll check it out in a bit.
Comment: Did you fix your problem? If so, don't forget to mark the answer as correct.
Comment: oops forgot to mark it. Thanks for the help this solved my problem.
Answer: Sorry if this reply comes a little late, but I rarely ever import into Unity, so I had to do a bit of trial and error.
First of all, there is nothing wrong with your file. The only thing that is missing is the link to your texture. If you load it back in via the Texture-Tab in the Properties Window, everything works as it should.

Consider packing your textures into the .blend files if you hand them off to somebody else, this will incorporate the images into the file and you will no longer have to send the texture files along with the .blend file.
Now, to import those files into Unity, there are a couple of workflows. I will give you the one that I find the most useful, if you want to learn about all the ins and outs, i would recommend Darrin Lile's course on Blender and Unity Pipelines. It is only about 12 Dollars, but it goes through all possible permutations of asset importing and gives you best practises to follow along the way. Like for instance naming the materials. It will not matter with a single cube, like in your file, but the materials do pile up.
Darrin Lile's Creating a Game Environment in Unity Course
To get assets from Blender into Unity follow these steps:

Set up the materials (like you have)
Export an FBX. Either for the whole Scene, or, with the "Selected" Checkbox checked, only the selected Objects
Drag these objects into Unity's Asset Window (or right click it and select Import New Asset)

I would recommend you set up 3 Folders: Models for the Mesh Data, Materials for the Unity Materials and Textures for the Texture files

If you use the same Texture Folder for your Unity Project that you use for your .blend files, you will not have to import anything here. It populates with the files that are in this folder.
Now select your object. It has the material on it, that you assigned in Blender. You need to hook up the brick Texture manually to the Albedo slot (see image above). Drag it from the texture folder onto the square next to the Albedo Label.

This should be all you need. I remember there was an option to embed textures into an FBX, but as far as I could find out, that ONLY works if you use Blender Internal Renderer and do NOT use nodes to build the material. Just wanted to mention it for completion's sake. FBX Export Article
Also, on import, the default color in Unity is an off-white, which will make your textures look less contrasty. To counteract this, set the base color to full white.


Tridion Rich Text Field Add CSS

Question: I have a rich text field, and would like to add CSS class to each underline of the the rich text content. Please suggest
Comment: Hello. Can you please give an example of what you would like the HTML to be both before and after the CSS class is applied please? Is the 'after' something like `Some text with a link` ?
Comment: Yes, currently I see text in the source of rich text field, I would like to have something like this, text
Answer: Rich Text styles can be configured in the CMS.
To do this you must

edit the FormatAreaStyles.css to add the styles you want.
Update the SDL version number.
Restart the Tridion CMS services.
Flush Browser Cache.
Then select the underlined text.
You can then select your styles from the Ribbon | Styles.
Answer: There are several different concerns at play here.
The first is functional: it's a standard convention on the Web to use an underline to identify a link. If you underline text that isn't a link, you may confuse a proportion of your visitors, so consider whether you actually want to do this at all.
Next is the format area itself. As Chris has said, you can make an underline style available via the Format Area style sheet. Then you'll have two mechanisms for underlining things, so you'll also want to disable the underline button in the toolbar. This is easy enough to do in the Allowed Actions tab of the Formatting features of the RTF in the schema, but then you've removed the obvious way of doing it and replaced it with a less obvious way. Sure - you can fix that too, by creating a GUI extension, but I'd argue that you shouldn't do any of this.
The third concern is what you actually want to have in your web site. There's no earthly reason why the web output needs to be identical with the representation in the Rich Text field itself. A Rich Text field actually represents the data as an XML document. This makes it relatively simple programatically to grab hold of the spans with the relevant style attribute and transform them to spans with a class. Where you do this depends on your architecture. If you're templating on the Content Manager, then you can make a template building block that does this, and in an MVC application you'd take care of this during or prior to rendering the view.
That's how I'd do it; just leave things as they are in the Rich Text field, and transform the data to the required output either in templating or in your application.

Tridion Rich Text Field Add CSS


What is an interface in Java?

Question: Just as a counterpoint to this question: what is an interface in Java?
Comment: [Interface considered harmful](https://blog.cleancoder.com/uncle-bob/2015/01/08/InterfaceConsideredHarmful.html)
Answer: An interface is a special form of an abstract class which does not implement any methods.  In Java, you create an interface like this:
interface Interface
{
    void interfaceMethod();
}

Since the interface can't implement any methods, it's implied that the entire thing, including all the methods, are both public and abstract (abstract in Java terms means "not implemented by this class").  So the interface above is identical to the interface below:
public interface Interface
{
    abstract public void interfaceMethod();
}

To use this interface, you simply need to implement the interface.  Many classes can implement an interface, and a class can implement many interfaces:
interface InterfaceA
{
     void interfaceMethodA();
}

interface InterfaceB
{
    void interfaceMethodB();
}

public class ImplementingClassA
    implements InterfaceA, InterfaceB
{
    public void interfaceMethodA()
    {
        System.out.println("interfaceA, interfaceMethodA, implementation A");
    }

    public void interfaceMethodB()
    {
        System.out.println("interfaceB, interfaceMethodB, implementation A");
    }
}

public class ImplementingClassB
    implements InterfaceA, InterfaceB
{
    public void interfaceMethodA()
    {
         System.out.println("interfaceA, interfaceMethodA, implementation B");
    }

    public void interfaceMethodB()
    {
        System.out.println("interfaceB, interfaceMethodB, implementation B");
    }
}

Now if you wanted you could write a method like this:
public void testInterfaces()
{
    ImplementingClassA u = new ImplementingClassA();
    ImplementingClassB v = new ImplementingClassB();
    InterfaceA w = new ImplementingClassA();
    InterfaceA x = new ImplementingClassB();
    InterfaceB y = new ImplementingClassA();
    InterfaceB z = new ImplementingClassB();

    u.interfaceMethodA();
    // prints "interfaceA, interfaceMethodA, implementation A"
    u.interfaceMethodB();
    // prints "interfaceB, interfaceMethodB, implementation A"
    v.interfaceMethodA();
    // prints "interfaceA, interfaceMethodA, implementation B"
    v.interfaceMethodB();
    // prints "interfaceB, interfaceMethodB, implementation B"
    w.interfaceMethodA();
    // prints "interfaceA, interfaceMethodA, implementation A"
    x.interfaceMethodA();
    // prints "interfaceA, interfaceMethodA, implementation B"
    y.interfaceMethodB();
    // prints "interfaceB, interfaceMethodB, implementation A"
    z.interfaceMethodB();
    // prints "interfaceB, interfaceMethodB, implementation B"
}

However, you could never do the following:
public void testInterfaces()
{
    InterfaceA y = new ImplementingClassA();
    InterfaceB z = new ImplementingClassB();

    y.interfaceMethodB(); // ERROR!
    z.interfaceMethodA(); // ERROR!
}

The reason you can't do this is that y is of type interfaceA, and there is no interfaceMethodB() in interfaceA.  Likewise, z is of type interfaceB and there is no interfaceMethodA() in interfaceB.
I mentioned earlier that interfaces are just a special form of an abstract class.  To illustrate that point, look at the following code.
interface Interface
{
    void abstractMethod();
}

abstract public class AbstractClass
{
    abstract public void abstractMethod();
}

You would inherit from these classes almost exactly the same way:
public class InheritsFromInterface
    implements Interface
{
    public void abstractMethod() { System.out.println("abstractMethod()"); }
}

public class InteritsFromAbstractClass
    extends AbstractClass
{
    public void abstractMethod() { System.out.println("abstractMethod()"); }
}

In fact, you could even change the interface and the abstract class like this:
interface Interface
{
    void abstractMethod();
}

abstract public class AbstractClass
    implements Interface
{
    abstract public void abstractMethod();
}

public class InheritsFromInterfaceAndAbstractClass
    extends AbstractClass implements Interface
{
    public void abstractMethod() { System.out.println("abstractMethod()"); }
}

However, there are two differences between interfaces and abstract classes.
The first difference is that interfaces cannot implement methods.
interface Interface
{
    public void implementedMethod()
    {
        System.out.println("implementedMethod()");
    }
}

The interface above generates a compiler error because it has an implementation for implementedMethod().  If you wanted to implement the method but not be able to instantiate the class, you would have to do it like this:
abstract public class AbstractClass
{
    public void implementedMethod()
    {
        System.out.println("implementedMethod()");
    }
}

That's not much of an abstract class because none of its members are abstract, but it is legal Java.
The other difference between interfaces and abstract classes is that a class can inherit from multiple interfaces, but can only inherit from one abstract class.
abstract public class AbstractClassA { }
abstract public class AbstractClassB { }
public class InheritsFromTwoAbstractClasses
    extends AbstractClassA, AbstractClassB
{ }

The code above generates a compiler error, not because the classes are all empty, but because InheritsFromTwoAbstractClasses is trying to inherit from two abstract classes, which is illegal.  The following is perfectly legal.
interface InterfaceA { }
interface InterfaceB { }
public class InheritsFromTwoInterfaces
    implements InterfaceA, InterfaceB
{ }

The first difference between interfaces and abstract classes is the reason for the second difference.  Take a look at the following code.
interface InterfaceA
{
    void method();
}

interface InterfaceB
{
    void method();
}

public class InheritsFromTwoInterfaces
    implements InterfaceA, InterfaceB
{
    void method() { System.out.println("method()"); }
}

There's no problem with the code above because InterfaceA and InterfaceB don't have anything to hide.  It's easy to tell that a call to method will print "method()".
Now look at the following code:
abstract public class AbstractClassA
{
    void method() { System.out.println("Hello"); }
}

abstract public class AbstractClassB
{
    void method() { System.out.println("Goodbye"); }
}

public class InheritsFromTwoAbstractClasses
    extends AbstractClassA, AbstractClassB
{ }

This is exactly the same as our other example, except that because we're allowed to implement methods in abstract classes, we did, and because we don't have to implement already-implemented methods in an inheriting class, we didn't.  But you may have noticed, there's a problem.  What happens when we call new InheritsFromTwoAbstractClasses().method()?  Does it print "Hello" or "Goodbye"?  You probably don't know, and neither does the Java compiler.  Another language, C++ allowed this kind of inheritance and they resolved these issues in ways that were often very complicated.  To avoid this kind of trouble, Java decided to make this "multiple inheritance" illegal.
The downside to Java's solution that the following can't be done:
abstract public class AbstractClassA
{
    void hi() { System.out.println("Hello"); }
}

abstract public class AbstractClassB
{
    void bye() { System.out.println("Goodbye"); }
}

public class InheritsFromTwoAbstractClasses
    extends AbstractClassA, AbstractClassB
{ }

AbstractClassA and AbstractClassB are "mixins" or classes that aren't intended to be instantiated but add functionality to the classes that they are "mixed into" through inheritance.  There's obviously no problem figuring out what happens if you call new InheritsFromTwoAbstractClasses().hi() or new InheritsFromTwoAbstractClasses().bye(), but you can't do that because Java doesn't allow it.
(I know this is a long post, so if there are any mistakes in it please let me know and I will correct them.)
Comment: One small remark, you call your class "InheritsFromTwoInterfaces", but when you use interfaces you are usually not speaking about Inheriting, but Implementing, this because the interface does not contain any logic and/or implementation you can inherit. Therefore it is better to speak about implementation (at least that is they learned me).
Comment: @Gertjan You are correct.  However, I don't think the distinction between "inherits" and "implements" is all that important, especially considering that in many cases one both inherits and implements an abstract class.  I chose to keep the naming scheme to be less confusing.
Comment: interface is like a pipe through which you can access to different classes of objects in a standardized way. Since in Java you cannot extend more than one class, interface is here to satisfy need for more complex inheritance.
Comment: No, interfaces are not used for inheritance. Interfaces are just "contracts" that define the functions and members an class must have when implementing the interface. Interfaces **cannot** be used to work around the "extend issue" (which does not allow you to extend 2 or more classes). when extending a class the functionality of the class you extend is still accessible (through the extending class), but since an interface has no functionality you cannot use it to ommit the multiple inheritance restriction because members and functions need to be written in the implementing class.
Answer: Interface is a contract. A simple example is a Tenant and Landlord which are the two parties and the contract is the Rent Agreement. Rent Agreement contains various clause which Tenants have to follow. Likewise Interface is a contact which contains various method (Declaration) which the Party has to implement (provide method bodies).Here party one is the class which implement the interface and second party is Client and the way to use and interface is having "Reference of Interface" and "Object of Implementing class": below are 3 components:(Explained with help of example)
Component 1] Interface : The Contract
interface myInterface{

 public void myMethod();

 }

Component 2] Implementing Class : Party number 1
 class myClass implements myInterface {

 @Override

 public void myMethod() {

 System.out.println("in MyMethod");

 }

 }

Component 3] Client code : Party number 2
 Client.java

 public class Client {

 public static void main(String[] args) {

 myInterface mi = new myClass();

 // Reference of Interface = Object of Implementing Class

 mi.myMethod(); // this will print in MyMethod

 }

 }

Answer: An interface in java is a blueprint of a class. It has static constants and abstract methods only.The interface in java is a mechanism to achieve fully abstraction. There can be only abstract methods in the java interface not method body. It is used to achieve fully abstraction and multiple inheritance in Java. An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface.
An interface is not a class. Writing an interface is similar to writing a class, but they are two different concepts. A class describes the attributes and behaviors of an object. An interface contains behaviors(Abstract Methods) that a class implements.
Unless the class that implements the interface is abstract, all the methods of the interface need to be defined in the class.Since multiple inheritance is not allowed in java so interface is only way to implement multiple inheritance.
Here is an example for understanding interface
interface Printable{
void print();
}

interface Showable{
void print();
}

class testinterface1 implements Printable,Showable{

public void print(){System.out.println("Hello");}

public static void main(String args[]){
testinterface1 obj = new testinterface1();
obj.print();
 }
}

Answer: Interface : System requirement service.
Description : Suppose a client needed some functionality "i.e. JDBC API" interface and some other server Apache , Jetty , WebServer they all provide implements of this.
So it bounded requirement document which service provider provided to the user who uses data-connection with these server Apache , Jetty , WebServer .
Answer: Interface is the blueprint of an class.
There is one oop's concept called Data abstraction under that there are two categories one is abstract class and other one is interface.
Abstract class achieves only partial abstraction but interface achieves full abstraction.
In interface there is only abstract methods and final variables..you can extends any number of interface and you can implement any number of classes.
If any class is implementing the interface then the class must implements the abstract methods too
Interface cannot be instantiated.
interface A() {
    void print()
}

Answer: This question is 6 years old and lot of things have changed the definition of interface over the years.
From oracle documentation page ( post Java 8 release) :

In the Java programming language, an interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Method bodies exist only for default methods and static methods. Interfaces cannot be instantiated—they can only be implemented by classes or extended by other interfaces.

Have a look at related SE questions for better explanation:
Is there more to an interface than having the correct methods
What is the difference between an interface and abstract class?
Answer: What it is
An interface is a reference type, just like a class is. These are the two main reference types in Java.
What it contains

An interface can contain a subset of what a normal class can contain. This includes everything that is static, both methods and variables, and non-static method declarations. It is not allowed to have non-static variables.

A declaration of a method differs from a normal method in several things; here is one as an example:
[public] [abstract] ReturnType methodName();

These declarations can be marked as public and abstract, as represented with [optional braces]. It is not necessary to do so, as it is the default. private, protected, package-private (aka. nothing) and the final modifier are not allowed and marked as a compiler error. They have not implementation, so there is a semicolon instead of curly braces.
As of Java 8, they can hold non-static methods with an implementation, these have to be marked with the default modifier. However, the same restrictions as to the other modifiers apply (adding that strictfp is now valid and abstract is no more).
What it's useful for

One of its uses is for it to be used as a face for a service. When two parties work together to form a service-requester & service-provider kind of relationship, the service provider provides the face of the service (as to what the service looks like) in the form of an interface.

One of the OOP concept is "Abstraction" which means to hide away complex working of the systems and show only what is necessary to understand the system. This helps in visualizing the working of a complex system.
This can be achieved through interface where in each module is visualized (and also implemented) to work through interface of another module
Answer: In general, we prefer interfaces when there are two are more implementations we have. Where Interface is acts as protocol.
Coding to interface, not implementations Coding to interface makes loosely couple.
An interface is a reference type in Java. It is similar to class. It is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. Along with abstract methods, an interface may also contain constants, default methods, static methods, and nested types. for more details
Answer: An interface is a class-like construct that contains only constants and abstract methods (Introduction to java programming, n.d.). Moreover, it can extend more than one interface for example a Superclass. Java allows only single inheritance for class extension but allows multiple extensions for
interfaces(Introduction to Java programming, n.d.) For example,
public class NewClass extends BaseClass
implements Interface1, ..., InterfaceN {
    ...
}

Secondly, interfaces can be used to specify the behavior of objects in a class. However, they cannot contain abstract methods. Also, an interface can inherit other interfaces using the extends keyword.
public interface NewInterface extends Interface1, ... , InterfaceN {

}

Reference
Introduction to Java Programming. Interfaces and Abstract classes (n.d). Retrieved March 10, 2017 from https://viewer.gcu.edu/7NNUKW
Comment: Be sure to use formatting options to be clear where you have code, and when explanations: `code` using `\`` and blocks `\`\`\``
Answer: From the latest definition by Oracle, Interface is:

There are a number of situations in software engineering when it is
  important for disparate groups of programmers to agree to a "contract"
  that spells out how their software interacts. Each group should be
  able to write their code without any knowledge of how the other
  group's code is written. Generally speaking, interfaces are such
  contracts.
For example, imagine a futuristic society where computer-controlled
  robotic cars transport passengers through city streets without a human
  operator. Automobile manufacturers write software (Java, of course)
  that operates the automobile—stop, start, accelerate, turn left, and
  so forth. Another industrial group, electronic guidance instrument
  manufacturers, make computer systems that receive GPS (Global
  Positioning System) position data and wireless transmission of traffic
  conditions and use that information to drive the car.
The auto manufacturers must publish an industry-standard interface
  that spells out in detail what methods can be invoked to make the car
  move (any car, from any manufacturer). The guidance manufacturers can
  then write software that invokes the methods described in the
  interface to command the car. Neither industrial group needs to know
  how the other group's software is implemented. In fact, each group
  considers its software highly proprietary and reserves the right to
  modify it at any time, as long as it continues to adhere to the
  published interface.
[...] An interface is a reference type, similar to a class, that can
  contain only constants, method signatures, default methods, static
  methods, and nested types. Method bodies exist only for default
  methods and static methods.  Interfaces cannot be instantiated—they
  can only be implemented by classes or extended by other interfaces.

The most popular usage of interfaces is as APIs (Application Programming Interface) which are common in commercial software products. Typically, a company sells a software package that contains complex methods that another company wants to use in its own software product.
An example could be a package of digital image processing methods that are sold to companies making end-user graphics programs.
The image processing company writes its classes to implement an interface, which it makes public to its customers. The graphics company then invokes the image processing methods using the signatures and return types defined in the interface. While the image processing company's API is made public (to its customers), its implementation of the API is kept as a closely guarded secret—in fact, it may revise the implementation at a later date as long as it continues to implement the original interface that its customers have relied on.
Check out to learn more about interfaces.
Answer:

In addition to what others have mentioned and by illogical comparison
it's a frame work for wrapping methods so they can be stored in
variables.

Thus on the fly you can equate the interface variable to be equal to any method or collection of methods atleast in this sense, a good reason you would usually want to do that is to escape repetitive logic that will definitely be an enemy of progress within the half life of your code at any decaying rate, be careful with the scenario below user discretion is advised.

SCENARIO
You have a game with a drawSillyThings() method in a SoulAvenger class, that has to draw some frames or sprites. Now drawSillyThings() has a list of other methods it needs to call in other to draw a metamorphed glorified-soul-ranger after user kills the grim-reaper in level 5k, i.e. drawSillyThings() needs to call either of inviteTheGrimReaper(), drawUpperCut(), drawTotalKO(), drawVictoryAndGlorifiedRanger(), drawDefeatAndMockery(), drawFightRecap() and drawGameOver() whenever the right situations arise during the gaming experience but all these would result in unwanted logic in drawSillyThings() which might slow the game i.e.
public static class SoulAvenger{

        public SoulAvenger(){
             //constructor logic
        }

        private void loadLevel5k(){...}

        private void dontAllowUserWinOnTime(){...}

        private void loadGrimReaperFight(){...}

        private void drawSillyThings(){
            ... //unaccounted game logic
            while(fighting_in_level_5k){
                while(soul_ranger_has_enough_lives){
                    if(game_state=fight)inviteTheGrimReaper();
                    else if(game_state=medium_blows)drawUpperCut();
                    else if(game_state=heavy_blows)drawTotalKO();
                    else if(game_state=lost)drawDefeatAndMockery();
                    else if(game_state=won)drawVictoryAndGlorifiedRanger();
                    else if(game_state=end)drawFightRecap();
                }else drawGameOver();
            }
        }
}

The problem here is the loop-nested boolean checks that have to be performed each time while the soul-ranger is still alive where as you could just have an alternative class which makes sure drawSillyThings() doesn't need a game_state to be checked each time in order to call the right method but to do that you 'ld need to kinda store the right method in a variable so that subsequently you can kinda variable = new method and also kinda variable.invoke(). If that wasn't something have a look
public static class InterfaceTest{

    public interface Method{
        public void invoke();
    }

    public static void main(String[] args){
        //lets create and store a method in a variable shall we
        Method method_variable=new Method(){
            @Override
            public void invoke(){
                //do something
            }
        };

        //lets call or invoke the method from the variable in order to do something
        method_variable.invoke();

        //lets change the method to do something else
        method_variable=new Method(){
            @Override
            public void invoke(){
                //do something else
            }
        };

        //lets do something else
        method_variable.invoke();

     }

}

This was probably what the guys at oracle had discovered was missing from Java several years before rumors of some developers planning a massive protest surfaced on the web but back to the SoulAvenger, as the gameplay occurs you would definitely just want to kinda have a variable be equated to give the right method to be invoked in drawSillyThings() in order to run things in a silly manner therefore
public static class SoulAvenger{

    private interface SillyRunner{
        public void run_things();
    }

    ...//soul avenging variables
    private SillyRunner silly_runner;

    public SoulAvenger(int game_state){
        //logic check is performed once instead of multiple times in a nested loop
        if(game_state=medium_blows){
            silly_runner=new SillyRunner(){
                @Override
                public void run_things(){
                    drawUpperCut();
                }
            };
        }else if(game_state=heavy_blows){
            silly_runner=new SillyRunner(){
                @Override
                public void run_things(){
                    drawTotalKO();
                }
            };
        }else if(game_state=lost){
            silly_runner=new SillyRunner(){
                @Override
                public void run_things(){
                    drawDefeatAndMockery();
                }
            };
        }else if(game_state=won){
            silly_runner=new SillyRunner(){
                @Override
                public void run_things(){
                    drawVictoryAndGlorifiedRanger();
                }
            };
        }else if(game_state=fight){
            silly_runner=new SillyRunner(){
                @Override
                public void run_things(){
                    drawFightRecap();
                }
            };

        }

    }

    private void loadLevel5k(){
        //an event triggered method to change how you run things to load level 5k
        silly_runner=new SillyRunner(){
            @Override
            public void run_things(){
                //level 5k logic
            }
        };
    }

    private void dontAllowUserWinOnTime(){
        //an event triggered method to help user get annoyed and addicted to the game
        silly_runner=new SillyRunner(){
            @Override
            public void run_things(){
                drawDefeatAndMockery();
            }
        };
    }

    private void loadGrimReaperFight(){
        //an event triggered method to send an invitation to the nearest grim-reaper
        silly_runner=new SillyRunner(){
            @Override
            public void run_things(){
                inviteTheGrimReaper();
            }
        };
    }

    private void drawSillyThings(){
        ...//unaccounted game logic
        while(fighting_in_level_5k){
            while(soul_ranger_has_enough_lives){
                silly_runner.run_things();
            }
        }
    }

}

Now the drawSillyThings() doesn't need to perform any if logic while drawing because as the right events gets triggered the silly_runner gets equated to have its run_things() method invoke a different method thus using a variable to store and invoke a method kinda-ish although in the real gaming world(I actually mean in a console) several threads will work asynchronously to change interface variables to run different piece of code with the same call.
Answer: An interface in java is a special type of Abstract class, the Interface provided the 100% Abstraction but since the java introduce new features in java 8 the meaning of whole Interface is change. Interfaces are used to tell what should be done. But due to new features now we give implementations of methods in Interface, that changed the meaning of Interface.
In Interface the method is public abstract by default
interface Bird{
        void sound();
         void eat();
        }

Java doesn't provide the multiple inheritances feature mean a class doesn't have two parents, but we extend multiple Interfaces in java.
Answer: An interface is a contract between the system and the external environment. More specifically to Java - a contract for a class (for a specific behavior), implemented in a form that resembles a pure abstract class.

What is an interface in Java?


What was the price of basic foodstuff in 1930 Poland?

Question: I'm working on a movie shot in Warsaw. The movie takes places in the 30s in Poland and we're currently searching for the prices of basic food during that time. Generally speaking, what was the price of thing likes a loaf of bread or soup seasoning in 1930 Poland?
Comment: I'm not sure that soup seasoning falls into the category of basic foodstuffs. Have you done any preliminary research?
Comment: I remember my grandma saying : 'you could get a meal in a restaurant for 1 złoty before the WW2 in Poland' ... . This was in inflation times in the 1980-ies ... .
Answer: I have data for 1939 at hand:

bread 30 groszy/kilogram   (kilogram = one standard loaf)
milk 26 groszy/liter
pork 1,50 zł/kilogram

The monthly wage for skilled industry worker was 95 złotych (1 złoty = 100 groszy). The wage varied considerably through 1930s due to some deflation. The purchasing power steadily rose, if 1928 is taken as 100, in 1938 it became 141 (source). There were no dramatic changes in prices through 1930s - no hyperinflation like in Germany.
Polish plurals:

1 grosz, 100 groszy
1 złoty, 100 złotych
Comment: One can find the złoty exchange ratios to different currencies in the interwar period on [this site](http://www.dobroni.pl/rekonstrukcje,przedwojenne-kursy-walut,13366), unfortunately in Polish, but I think easy to understand
Comment: +1 for giving a frame of reference for the price by providing the wage as well.
Answer: This might help you get a basic understanding of how much stuff cost back then.
Thank you http://www.polishsite.us/index.php/history-and-people/modern-history/458-reflections-from-the-great-depression-in-poland-1930-1936.html
Current economic crisis encourages us to reflect on economic depression of the 30s. In Poland the economic crisis started slightly later than in the US, but it lasted longer: 1930-1935.  From the perspective of the World War II which followed Poles tend to see thirties as good years. But the big economic crisis brought lots of misery and poverty, especially in the regions which were poor already, mainly in Southeastern Poland.
Both of my parents were born in 1930. They were still children in the pre-war times.
My father came from relatively rich family, he was the only child. He grew up partly in the country. He still remembers that the cheap food products made farmers very poor.  But the real misfortune did not affect his family until the WW II when his mother died on tuberculosis, which was accelerated due to the poor diet. They ate mainly rapeseed soup and rye bread. During the war the medical care was also inadequate.  My father became semi-orphan as 12 years old boy.
My mother was the youngest from seven children in a miner's family in Katowice, Upper Silesia. When she was born the whole family lived in a house which consisted from a kitchen and two rooms, but they only has the access to one room. Like many Poles they had also a small farm with geese, chicken and goats and a small field and garden. Her father, a miner, was forced for early retirement during the Great Depression. He lost much his savings in a bank bankruptcy. Still, my mother's parents were able to expand the house adding the upper floor. Of course, during this time they had to save on food, so the meat or buttered bread was only served on Sundays.
My mother remembers that during the crisis her family had to guard against the thieves. They were sitting in the fields nearby smoking cigarettes. One could see the small blinking lights from their cigarettes. These thieves sometimes stole a chicken or goat. Once they even stole a family dog after they put him to sleep.
There were many poor people and beggars asking for help. My grandmother has never sent anybody away without anything to eat. There were also men who were collecting rags in exchange for some small gifts. My mother remembers to get a child ring for some old rags her family gave away.
In general, years 1926-1928 were successful for Polish economy. The export grew, especially coal export due to the long strike of British miners. The unemployment was low. But the economic crisis affected Poland quite soon after the New York stock crash. Foreign banks withdrew credits given for development of Polish economy, the foreign investments stopped. The crisis affected the most agriculture which was giving jobs to 60% of Poles. In 1929 Polish economy was in 79% agrarian and in 21% industrial. This was one of the main reasons why Polish crisis was longer than in industrially developed countries.
The first sign of the crisis was a drastic decrease of the food prices due to overproduction and decrease of the consumption by urban population. Farmers had to sell much more products to pay taxes, buy tools, cloths, salt or matches. The lower food prices and higher supply caused further decrease of food prices and more hardship for farmers. With a time it led to a high inequality between food, very cheap, and industrial products, very expensive.
The industrial slow down caused rapid decrease in production. This led to the development of monopoles which limited the competition and led to increase in prices.
economical crisisThe total industrial production in 1932 was about 40% less than in 1928. 1932 was the worst year for Polish economy, the unemployment beyond farming was estimated at 44%.
Initially Polish government did very little to improve the economic situation besides fighting for duty barriers for imported products and for easing of barriers for Polish products. The course of Polish currency was kept high, the access to the credit was low, the investments were low and the budget expenses were cut. This led to lower industrial production, lower prices and lower standard of life of population. The more complex program to fight the crisis was introduced at the end of 1932. It helped to increase the value of farming products and to lower the prices of industrial goods, especially these produced by monopoles. The government initiated steps against unemployment and to increase the export. People were hired for public works. My mother remembered that some barracks which were build for temporary road workers. The safe work for many people was a job in public institutions. The lowering unemployment decreased the number of strikes. Many corporations become public, since they were unable to repay their credits.
Industrial projects were kicked off to alleviate differences between better developed western and central Poland, so called "Poland A" and poor "Poland B" which included Easter and Southeastern regions, predominantly a farmland inhabited by minorities. The biggest project was so called Central Industrial Region (COP) was initiated in 1936 in the central Poland just between Poland A and Poland B. The COP project was interrupted by the outbreak of War World II in September 1939. One has to wonder how Poland would look like in the present time if not the biggest human and economic devastation and then forty years of communism brought by the war and Soviet occupation.
Comment: It seems very paradoxical to me that they had to spare on food, but that food was very cheap.
Comment: I'm sorry kubanczyk but I tried my best to get some information about food prices in Poland in 1930


Is it possible record videos of my screen?

Question: Suppose that I would like to record some video sessions of Angry Birds on my phone.
Are there any apps that I can use? I have root permissions.
Answer: I just read a review of Screen Cast & Screen Recorder that's pretty compelling.  It requires root, like any on-device solution I'm aware of, but can record decent quality video at up to 30 FPS.  The review has example captures from various games and the videos are good enough for most anything you'd want, unless you need HD video for some reason.  The app has a free trial so I definitely recommend trying it out.
Answer: Yes you can, even without root, by using adb, ddms, and DroidEx. See: http://answers.oreilly.com/topic/951-how-to-capture-video-of-the-screen-on-android/
The basic idea is to use ddms to capture a screenshot rapidly, and then composing these screenshots into videos.
I haven't actually tried this yet, so I don't know how well it works (or whether it works).
I doubt this can be done practically purely in device-side; problem being that video is extremely memory heavy without compression, and compressing video in real time will be a torture to even the latest phone's CPU.
Comment: The link for this is dead.
Answer: Airdroid has a "Record Screen" option. It's not a premium feature and doesn't require root. It records the screen along your microphone (warning! As far as I remember this option is set by default!) if you do like to make tutorial videos.
Answer:
Some of my friend use this app I think it will work you too.
 Here is the link


Under-extrusion in vase mode

Question: So I found a vase on thingiverse and I wanted to print it, so obviously I did. I used craft ware to slice the model using there 'vase mode', and sent the Gcode to my Anet A6 printer. In the end I found weird underextrusion (I think that is what happened) at the starting points that seem to have appeared. I don't know what to think of this and I don't know what happened or how to fix it.
Comment: @CarlWitthoft I changed it, sorry for not making sense, hopefully it is better now! Thank you for pointing that out
Comment: Your question is rather like the " My car doesn't work. Fix it" command to a repair shop.     We're not mind readers:  tell us your printer model, the software you're using to slice,    Try also to edit your post so it's in temporal order. As it stands it's impossible to tell what worked and what didn't.
Answer: This sort of failure is best diagnosed by observing the failure. It probably isn't underextrusion, there is no reason to get variation in extrusion just along one edge.
Did you really get a proper vase-mode? You can check in your slicer, or with gcode.ws and make sure that each layer only occupies a fraction of the part, with many small steps (rather than one step after printing a slice of the whole part)
It seems the failure is close to a sharp transition in the wall. Have you got enough cooling, or a low enough extrusion temperature? It could be that the plastic viscosity and surface tension are conspiring against the shape. Printing slower might possibly help too (both on the failure, and to allow the part to cool between layers).
Finally, you might have a mechanical problem which is interfering with the print just at this point, and that might include the extruder binding in some way. This could be hard to spot during the print, so check over all the moving parts, and all the fixings.

Under-extrusion in vase mode


How to convert SMART-PLS structural coefficients from standardized (correlation) to unstandardized?

Question: I need use smartPLS but i also have prediction purpose (coefficients should also act like b-coefficients of regression). How to do this in smartPLS, since all coefficients are standardized?
Answer: In SmartPLS, you can get unstandardized path coefficients in the IPMA (importance-performance map analysis) analysis. Follow these steps to run IPMA in SmartPLS (v.3):
First, select IMPA from the 'Calculation' menu

Second, select a dependent variable as the target (SAT in this example)

Third, open the report and click 'Latent Variables' to see the scores

Fourth, by default, you will see standardized scores. Click on 'Unstandardized'

Fifth, you will find what you are looking for here. In this example, the survey response scale was a 1-7 Likert. Therefore, the unstandardized scores are in the range of 1-7.

More about IMPA analysis in SmartPLS:

Introductory information about IMPA analysis is available on the SmartPLS website.

This article offers some details on how to report IMPA analysis; see Web Appendix W9 for a detailed discussion. This is an open-access article.


Naming convention for actually choosing the words in Python, PEP8 compliant

Question: I'm looking for a better way to name everything in Python.  Yes, I've read PEP8, Spolsky's wonderful rant, and various other articles.  But I'm looking for more guidance in choosing the actual words.
And yes I know

A Foolish Consistency is the Hobgoblin
  of Little Minds.

But, you can keep consistent with PEP8 etc, and still not have consistent variable/method/class names which are easy to remember.  By consistent, I mean that if you were presented with the same decision twice, you would produce the same name.
As an example, there are multiple PEP8 compliant ways to name the items below:

number of columns in the table
current column number
column object
sum of column

Yeah, sure, it is easy to make a decision to use something like num_col and count_col rather than col_num and col_count (or v.v.).  But, I would like to see an example that has seen some testing/refining over time. I often start with a given convention, and then it starts to break down as I venture into a new area.
I guess what I am looking for is not only what the prefix/root/tag/suffix should do (which was partly covered for Apps Hungarian in the Spolsky article), but (many) examples for each, or a rule for generating each.
Answer: I believe that the need for complex variable naming conventions goes away with good object-oriented design. In the Spolsky article, much focus is on how variable naming helps preventing errors. I believe that those errors will more often occur when you have many variables in the same scope; this can be avoided by grouping data into objects - then, a single naming context will have only few variables, which don't need combined names.
The other purpose of a naming convention is to better remember the names. Again, object-orientation helps (by hiding much data from users that look from the outside); what you then need is a convention for naming methods, not data. In addition, tools can help which provide you with a list of names available in a certain scope (again, those tools rely on object-orientation to do their job).
In your specific example, if column is an object, I would expect that len(table) gives me the number of columns in a table, sum(column) or column.sum() gives me its sum; and the current column is just the variable in the for loop (often c or column).
Comment: Good point about focusing on minimizing the number of variables in any given scope.  It certainly helps, but as you point out, method naming is still an issue.  Especially when using modules which you haven't used for a long time.  A good IDE can help only so much.
Answer: Remember that in English, when two ambiguous words are next to each other, the first one becomes an adjective which describes the second one. Try to stick to this rule and always name things with two components where the first component decribes the second.
For instance col_num is a number. What kind of number? A column number.
Next rule is the word of. It is a nice short word so please do not leave it out. Same goes with pluralization. And past tense ending in -ed or -d. Maybe even -ing.
For instance, num_col is a column. What kind? A number column. If you really wanted to refer to the number of columns, you should write num_of_cols. Received date is recd_date or rcvd_date, not rec_date or rcv_date.
English speaking readers are very sensitive to -s and -d at the end of words, as well as of in the middle of a phrase, so don't assume that such short bits of text would be missed. That is very unlikely because we are programmed from a very young age to notice a handful of word endings.
Try for consistency, and keep a glossary or data dictionary of any words, or word fragments that you use. Don't use the same fragment for two different things. If you are using recd to mean received, and you need a variable name for recorded, then either write it out in full or come up with a new abbreviation and put it in the glossary. If you use a relational database, try to be consistent with the naming convention used there. Let the dba know what you are doing and tell them where to find your glossary.
Answer: The universe is multi-dimensional.
You have at least two dimensions to each variable name.
"Total", "Count", "Of Columns", "In a Table"
"Current", "Index", "", "Of a Column"
"Current", "Column", "", ""
"Sum", "Of Something", "", "In a Column"
Rats.  It's irregular.
Worse, we can pick anything as the "Primary" dimension and pick any sequence of other features as "secondary" dimensions.
Even worse, we could have a truly complex thing.  "Total", "Count", "of Non-Underscore", "Columns", "In Tables", "With Even-Length Names", "From a Dictionary", "Keyed by", "Mother's Maiden Name".
Frankly, there's no possible schema for variable names that encompasses "all" knowledge in a systematic, repeatable form.
Keep trying though.  It's always fun and games until someone finds a counter-example.
You can keep trying or you can simply use simple, clear names.  If your scope of names is small (a small method function, for example), there's nothing to "remember".  It's all perfectly visible in the 20 lines of code that make up the method function.


Gauss law - charge inside a conductor

Question: If there is a point charge inside a shell conductor for example, making a Gaussian surface around the point charge will tell me there is a non-zero flux, meaning non-zero electric field inside, but how is that possible if electric field inside any conductor is zero because charges on the inner surface redistribute to cancel the electric field?
Comment: But that point charge is in the cavity, so what's the problem in having an electric field inside the cavity?
Answer: When we say that the net electric field inside a conductor is zero, what we mean precisely is that it is zero inside the meat of the conductor. When you put the point charge inside, the electric field was precisely zero between the inner and outer surface of the conductor. The inside part(where the charge is present) is not the meat of the conductor.
Comment: Why doesn't the point charge in the cavity induce a charge distribution on the inner surface of the conductor that will cancel the field inside?
Comment: Simple answer- Because it can not. There is no reason why it would be able to do so. For every arbitrary gaussian surface you draw inside the cavity, the net charge inside would be $q$ since there can be no inductions in free space. So, since $$\displaystyle \int \textbf{E}.\textbf{ds} \neq 0$$ for any arbitrary surface, electric field has to be non zero any way.
Answer: Metals have access to a sea of free electrons. Under equilibrium condition the net movement of the electrons inside the metal is zero. And this is reflected in the fact that metals have no field inside them.
To answer your comment:

Why doesn't the point charge in the cavity induce a charge distribution on the inner surface of the conductor that will cancel the field inside?

Simply because the charge distribution at the inner surface is such that the field in the metal is zero. This need not balance the field in the cavity.
Answer: The electric field inside a conductor is zero in a static situation. Static means, when the charges are in rest. When there's an electric field inside a conductor, the free electrons will move until the electric force (and thus the electric field) acting on them becomes zero.
Answer: You are giving 2 situations in 1st case when there is a sphere with uniform charge density there must be charge inside the gaussian surface which means there must be an electric field
CASE 2
In case I of conductors the charge electric field inside the conductor has to be 0 so all charge in a conductor resides on the surface . The charge enclosed in the gaussian surface conductor becomes 0

Gauss law - charge inside a conductor


Terminology - entry point, data source, sink

Question: In the context of application security, I often heard the terms entry point, data source and sink.
Can you define them for me in simple terms please?
Answer: Source and sink are used in a data flow analysis. The source is where data comes from, the sink is where it ends. With regards to application security, source and sink are frequently used for taint analysis.
Data is "tainted" if it comes from an insecure source such as a file, the network, or the user. Any data that touches data also becomes tainted. If tainted data is ever passed to a sensitive sink, then static analysis will flag an issue. For example, if user input from a web form is printed, unescaped, into a log file, then a static analysis tool will report a log forging vulnerability.
I think that entry point is a more general term that refers to the place where a program or event handler begins execution. For example, the main() function of a C program or the doGet() function of an HttpServlet. This is the starting point for data flow analysis.
Comment: Thank you sir for your answer. If data is passed between multiple functions func1 -> func2 -> func3. Are all functions in this path, sinks?
Comment: Generally, sink is the end of the data flow. In the context of security static analysis, sinks are the operations that must have clean data. A sink could be a database call or returning data to the browser. Anything that you wouldn't want an attacker to be able to fully manipulate. You use *sanitizing* operations to escape or filter tainted data. After sanitization, tainted data becomes clean and can safely enter a sink


volume of a torus

Question: I hope that this question has not been answered yet.I want to find the volume of the following set. I think it is a torus but I am not entirely sure.The set of points is:
$\{(x,y,z)\in\mathbb{R}^3:x^2+(2-\sqrt{y^2+z^2})\leq1\}$
My first idea was that it is a circle that is somehow shifted by to units along one axis.I am a bit puzzeled about the following term:
$(2-\sqrt{y^2+z^2})$
what does it do?
Thank you very much in advance for your help!
Comment: I think this is no torus. It is unusally, that $x$ enters quadratically and $y$ and $z$ do not.
Comment: Maybe there is a typo?
Answer: Your set is $x^2+1 \le \sqrt {y^2+z^2}$ or $(x^2 + 1)^2 \le y^2+z^2$  This is unbounded in $y$ and $z$, so you cannot compute its volume (or just state that it is infinite).
Answer: It is not a torus.
I'll rearrange the inequality:
$$\sqrt{y^2+z^2}\ge x^2+1$$
which is the set of points in $\Bbb R^3$ which distance to the $X$ axis is greater than or equal to $1$ plus the square of their $x$ coordinate.
Making $z=0$ we get
$$|y|\ge x^2+1$$
that gives two symmetrical parabolas and their "inside". The set of points that you have asked about is obtained as the revolution of these two parabolas along the $X$ axis, some sort of an infinite doughnut (the radius of the hole is $1$).
Answer: Assume there's a typo (please ignore this answer if there is no typo) and that the equation should read
$$x^2+(2-\sqrt{y^2+z^2})^2\leq 1$$
which is the equation of a torus with radius of locus of cross-section centre (is there better term for this?) of $c=2$, and radius of cross-section of $s=1$.
By Pappus' centroid theorem, the volume of the torus is given by the cross section multiplied by the distance travelled by its centroid, i.e.
$$\begin{align}
V&=\pi s^2\cdot 2\pi c \\
&=\pi(1)^2\cdot 2\pi(2)\\
&=4\pi^2\qquad\blacksquare \end{align}$$

volume of a torus


How to Restrict user to select single selection from Multiple selection List Box in Infopath 2010

Question: I'm using Infopath 2010 and created form with Multiple Selections in List Box. I want to restrict users to single selection only. How do i acheive this without any coding.  I'm from non-technical person. Just working on some process efficiency using Infopath.
Answer: Should the item only ever have one selection? You could simply change the field to not allow multiple values from within SharePoint. Easiest way to make sure the form updates properly after the change is to adjust the field in the library on SharePoint, then select the 'Customize Form' button to start editting the infopath form -- it should prompt you that the field definitions have changed and you need to update them.
Comment: Hi John, yes, Item will have one selection ever. I thought of doing so but i have created some rules and conditions to autofill employee name using Infopath. If i use the sharepoint form to change the settings and load it again in Infopath will the previously created rules and conditions will purge off or will stay same.. As i said i'm not from technical background so not sure of these things.
Comment: @kumarchenna The original control you created in your infopath form will no longer work, however it will remain available on the form, so you could copy all of the rules from the old control (multiple value) to the new control (dropdown or combobox probably) using the 'manage rules' pane -- then you would just need to delete the old multivalue control