Is this plagarism? (Maths assignment) EDIT: Could the downvoter please let me know if I should improve my question in some way. For clarity, I am asking whether what I describe below is considered plagarism, and if so what the approporiate course of action to take is.
I am very concerned about an assignment I submitted recently for mathematics, and that I may be accused of plagarism. The assignment consisted of several questions. For a part of one of these, I had come across something similar in a slightly different context in a talk I had given a couple of weeks earlier. It was just an aside around the reading I was doing- it was actually a named theorem, but at the time I didn't register it, but I remembered gathered the sketch of the proof and moved on. With this proof, it is of the form that when you frame the problem in the right way, then the proof just flows and it isn't really possible to modify it in any way. It also seems fairly general- I didn't read it in a paper, it must have been on some general expository website on topics relating to my area of math or a blog post.
So I used this framework for my problem (I iterate was in a different context) and wrote up the proof. At the time, I had a small thought as to whether I should try to track down a source similar to whatever it was that I had come across in preparing the talk. For some reason I decided that it was unecessary because it was just a framing of the problem that I started arriving at myself (which is why I recognised the connection to this different context) and secondly because, as noted above, it seemed like something fairly standard that one might come across in a course on the topic.
But now I am panicking for two reasons. Firstly, I feel that I have not given proper credit to the person who came up with this framing of the problem and proof in a different context (even if it is standard now, it was not once in the past). Secondly, as mentioned above it is essentially impossible to modify the proof once you have the framing, so what I wrote looks very similar to other sources. Heck, now that I've been panic checking for this theorem online, I've found pages\lecture notes which actually use almost exactly the same notation as me because the choice of notation is very natural.
I feel sick to my stomach, and feel compelled to write to someone to say that the idea for the proof was from elsewhere, but I do not know if this will help the situation. I was very tired and writing up the assignment in a bit of a rush before the deadline, so I was less vigilant about referencing than I should have been. As an aspiring academic, I am absolutely disgusted with myself that I did not give proper credit to whoever came up with this proof first just because it felt 'standard' and 'assumable', like the kind of toolbox set of techniques one picks up in a course.
Whatever the official outcome will be, I have learnt my lesson simply because of the anxiety and worry I feel now. But I would appreciate some advice on this. I'm finding it hard to judge myself if what I did was wrong or not, because this is mathematics. What distinguished 'copying a proof' from 'having read the proof at some point in the past and acquired the gist as a useful technique that I am now applying'? I am quite confused.
Contact the professor now, if for no other reason than to get out of your panic spiral.
Let them know that you are concerned that you failed to appropriately cite your sources and that you are generally confused about what can be treated as assumed knowledge and when you should credit a source.
You could even go as far as submitting a version of your assignment that does cite sources more completely.
This can be a learning experience. Go ahead and be an active part of that process.