So I'm studying projective geometry and I'm confused about duality. In particular, I'm confused about drawing dual pictures. If you look at Menelaus's Theorem and Ceva's Theorem, they are supposedly dual diagrams. http://en.wikipedia.org/wiki/Menelaus'_theorem http://en.wikipedia.org/wiki/Ceva's_theorem In the diagram for Menelaus's theorem, there are 6 points and four lines, so that means that there are 6 lines and four points in Ceva's theorem. However, looking at Ceva's theorem, there are indeed 6 lines but there are more than 4 points, there are 7. So how can they be dual diagrams?