TITLE: Do I need to cite an old theorem, if I've strengthened it, wrote my own theorem statement, with a different proof?
QUESTION [25 upvotes]: Let's say I have been studying an older theorem statement and its proof.  I feel that it can be improved, e.g., I can make it a stronger double-implication theorem statement, with a different proof.  Would I still need to cite the paper from which I first studied the theorem?  Even though my work is completely organic and self-contained?
Thanks,

REPLY [43 votes]: Adding this only because I think the point wasn't emphasized enough in the other answers, but it may actually hurt the credibility - or, at least, the perceived professionalism - of your paper if you did not cite the old result. An important part of research is to establish context and relevance, and anyone who happens to know or find the old result might (wrongly) conclude that you didn't carry out that part as expected if you didn't cite the prior work.