Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 77
PJ. (A, E) Proof. This follows almost immediately from the theorem, exceptwhen it happens that a set of four successive lines of the set lxl2l3 • • • lnare such that the first and third coincide and likewise the second andfourth. That this case forms no exception to the corollary may beshown as… … A = A3 B, B3Fig. 25 Q and l2 in A2; let Az = Ax and Ai be the corresponding points of l3 andZ4 respectively. Further, let Bx, B2, B3, Bi and Cx, C2, C3, C± he anyother two sequences of corresponding points in the perspectivities.Let SiX be determined as the intersection of the lines AXA± and…
Geometry, Projective
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