Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 337
lllines linearly dependent on the lines of these two congruences. The 322 FAMILIES OF LINES [Chap. XI directrices of the two congruences intersect at B and P3i respectivelyand determine two planes, ah = p and ah = ir, which meet on q. Through any point P of space not on p or ir there are two… … Fig. 115 points and thus determines a projectivity between the flat pencil ah and the fiat pencil ah, in which a and a, h and V correspond and a corresponds to itself. The projectivity thus determined between the pencils ah and ah is the same for all points P, because a, h, q always correspond to…
Geometry, Projective
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