I am supposed to know how to use Zorn's Lemma on a final exam of the course Discrete Math, but I only had a few chances to practice it (and only about 1 of them were by me, only).

Where can I find questions about Zorn's Lemma, or ways of using it in order to solve problems?

I tried to google it - but didn't really find anything useful, and thought that some of you might know some nice questions that require the use of Zorn's lemma..

Thank you very much!