Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 228
ctivity on a conic. ■ Theokem 8. Two conies that are projective with a third areprojective. Proof. This is an immediate consequence of the definition and thefact that the resultant of two collineations is a collineation. We proceed now to prove the fundamental theorem for projec-tivities between… … Proof. Let C2, C2 be the two conies (fig. 86), and let A, B, C &ethree points of C2, and A, B, C the corresponding points of C2. LetP and P be the poles of AB and AB with respect to C2 and C1respectively. If now the collineation ir is defined by the relation7r(ABCP)=ABCP (Theorem 18, Chap. IV),…
Geometry, Projective
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