Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 36
is a point of 7r, whichreduces the proof to Case 3. It may be noted that in thisproof no use has been made of E 0. In discussing Case 4 we haveproved incidentally, in connectionwith E0 and Theorem 4, the fol-lowing corollary: Corollary 1. If Sg is a three-space determined by a point P and aplane… … Fig. 11 22 THEOREMS OE ALIGNMENT AND DUALITY [Chap. I Proof. As before, let the three-space be determined by ir and P,and let the three noncollinear points be A, B, C. Every point of theline BC is a point of S3 (Theorem 8), and every point of the planeABC* is collinear with A and some point of BC.…
Geometry, Projective
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