I just made my first visit to your web site the other day (I enjoyed it immensely!) and decided to do a project/presentation on the Menelaus Thm for my Conjecture and Proof course at Goshen College. This required an in-depth analysis of the proof(s) and in writing my paper, I noticed that the proofs on your site only proved "If the points are collinear, then AF/BF * BD/CD * CE/AE = 1," but the theorem is in an "if and only if" form. We learned in Conjecture and Proof class this semester that for an iff statement, the proof must prove, "If AF/BF * BD/CD * CE/AE = 1, then the points are collinear" also. Is the backward step so obvious that it wasn't needed and I missed something, or ...?

Thanks!

Sarah Amstutz