During study , I am encountered with this two Inverter symbols .  Sometimes this two symbols are usedn in same logic circuit. Though they are working as inverter, I'm guessing there must be some charecteristic differences indicated by this two symbols.Or there is no logic to use two different symbols in same circuit.  Is this symbols indicated different kind of inverters or some different physical properties  ?
See , page 2: the internal logic diagram for the MM74HC138.    The diagram shows logic inverters with bubbles at the input or at the output. Is there an actual difference between them?
What is the relationship between lands and mana in Magic and what do each of them do?  A good answer should especially include how a new player should think about them.    Note:  This is an attempt to create a canonical question about the relationship between lands and mana in Magic.  Beginners are often confused about this given the same symbols are used to mean different things across basic lands, non-basic lands, and mana costs.  This can lead to confusion about , about , or even about .