Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 231
of the pencil of points.A line conic and a pencil of linesare said to be perspective if everytwo homologous lines meet in apoint of a pencil of points whoseaxis is a line of the conic. The reader will now readily verify that with this extended use ofthe term perspective, any sequence of… … Fig. 87 perspective with the same pencil of lines or with the same pencil ofpoints are projective by Theorem 10, Cor., etc. Another illustration of this extension of the notion of perspectivityleads readily to the following important theorem: Theoeem 11. Two conies which are not in the same plane…
Geometry, Projective
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