A highly regarded professor of mine is currently writing a graduate mathematics textbook in which he has given the book a theme of ``do it yourself'' mathematics.
He has asked me to review the book in its early drafts, and one thing I've noticed is that some one the theorems that are left for the reader to prove would benefit from a simple spoiler in the spirit of those on math.se
For example, a good use of the spoiler's functionality can be found here.
So, my question is whether or not it is possible to implement this functionality in pdf documents.
Theorem 4.5: There are infinitely many primes.
! Suppose there were finitely many primes. Multiply them together and add 1. What can you say about this new number?
Thanks for you help.