Veblen, Oswald, 1880-1960, Young, John Wesley, 1879-1932 · Boston, New York [etc.] Ginn and Company · leaf 144
fconies of Type I (fig. 61). Theorem 19 and its plane dualTheorem 22. Any line (notthrough a vertex of the deter-mining quadrangle) is met by theconies of a pencil of Type I in thepairs of an involution* Definition. The set of all coniestangent to the sides of a completequadrilateral is called a… … Fig. 63 Corollary. Through a gen-eral^ point in the plane there isone and only one, and tangent toa general line there are two or noconies of a given pencil of Type I. Fig. 64 Corollary. Tangent to a gen-eral line in the plane there is oneand only one, and through a gen-eral point there are two or…
Geometry, Projective
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