Coxeter- Figure 7.1A
Let p and q (through C) be the polars of two self-conjugate points P and Q on a line c. Let R be a point on p, distinct from C and P. Let its polar r meet q in S. Then is the pole of , which meets r in T. Also is the pole of , which meets c in B. Finally, is the pole of , which meets c in A, the harmonic conjugate of B with respect to P and Q.