There are several Pappus' Theorems. But this is the famous one. It
is also called Pappus' Hexagon Theorem. If A, B, and C are three points on a
line, and D, E, and F are three points on a second line. And AE meets BD at X,
and AF meets CD at Y, and BF meets CE at Z, then X, Y, and Z are colinear (on a
straight line).