Coxeter-Statement 8.11

Topic:
Geometry
8.11: Any two conjugate points on a secant PQ are harmonic conjugates with respect to P and Q. The converse and dual of this statement is also true. On Figure 8.1 B, on a secant PQ, the involution of conjugate points is (PP)(QQ). Hence the above statement (8.11) follows from statement 5.41.