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Collineations of an affine geometry

  1. Mar 3, 2010 #1
    An affine geometry is a nonempty set of points A, together with a set of lines, where each line connects one or more of the points in A.

    A collineation of A is a bijection f: A --> A that carries lines to lines. That is, if P,Q are points in A lying on the same line, then f(P), f(Q) are points in A lying on the same line.

    My question:

    Does this definition imply that each pair of points not lying on the same line is carried to a pair of points not on the same line? That is, if P, Q do not lie on the same line, then do f(P) and f(Q) also not lie on the same line?
  2. jcsd
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