# Coxeter- Exercise 5.3.1

- Author:
- AndrewLyon

- Topic:
- Geometry

Exercise 5.3.1 Given six collinear points

*A, B, C, D, E, F,*consider the three involutions*(AB)(DE), (BC)(EF), (CD)(FA)*. If any two of these involutions have a common pair, all three have a common pair. Drag any one point O, O1, or O2 onto another one of those points or stack all three, at least two of the involutions will have a common pair forcing the third to be in common with the other two as well.