I apologize for the vagueness of the topic title. Allow me to clarify what I mean. Let's say a professor is explaining a theorem while proving it on the board. He is explaining this to a fairly small class; he would hypothetically know what every single student is at his or her desk. Suppose there is some student who begins to write (or finish) his own version of the theorem that the professor is in the middle of proving. Would it be disrespectful, because the professor might be made to feel slightly redundant? Is this the sort of behavior that should be avoided in a college classroom environment?