In the syllabus (under "Rules of the Game"), I wrote
You should not look to resources outside the context of this course for help. That is, you should not be consulting the web, other texts, other faculty, or students outside of our course. On the other hand, you may use each other, the course notes, me, and your own intuition.
The spirit of this "rule" is to discourage "looking up answers." I want the emphasis to be on us creating mathematics. However, I am perfectly okay with people looking up things like "how do I prove something by contradiction?" or "what's the contrapositive?" or "what's the definition of a function?" I hope you get the idea and if I need to be more explicit, just ask.