Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 329
f the flat pencils, we have, byduality, the case just considered. If a meets the common line of thetwo flat pencils in a point distinct from the centers, the two flatpencils may be regarded as determined by their common line d andby lines V and c, one from each pencil, not meeting a. Hence… … Fig. 112 If a does not meet the common line, it meets the planes of thetwo pencils in points C and D. Call the centers of the pencils A andB (fig. 112). The first pencil consists of the lines dependent on ADand AB, the second of those dependent on AB and BC. As CD isthe line a, the family of lines…
Geometry, Projective
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