# Coxeter- Exercise 2.5.1

According to the figure, try to look for any line with four points on them. We can see that line e has points Q,G,P,F on it.P and Q are diagonal points for a new quadrangle EDHS. The harmonic set is H(QP,GF). Also, line f has points R,G,S,C on it. R and S are diagonal points for a new quadrangle PJIK. The harmonic set is H(RS,GC).

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