Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 103
Then if I meets the lines of R1 and R2 in ij* and P2 respectively, thequadrangle PQA1B1 gives rise to the quadrangular set Q(P2A2B2,OB2A2) of which five points are points of R2; hence P2 is a point of R2(Theorem 9). Px is then a point of Rx by the first case of this proof. Theorem 11. The… … Fig. 39 Proof. This follows directly from the definition and the last theo-rem, except when one of the lines passes through 0, the^oint commonto the two linear nets R15 R2 defining the planar net. In the lattercase let the two lines of the planar net be lv l2 a^d suppose l2 passesthrough 0, while…
Geometry, Projective
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