Lemma 3 If tεA(2) fixes every point of the line L, and sεA(2), then u = sotos-1 fixes every point of s(L). Proof For Pεs(L), P = s(Q) for some Q on L, and so t(Q) = Q. Then u(P) = sotos-1os(Q) = sot(Q) = s(Q) = P.

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