real projective plane

Noun

 * 1)  A three-dimensional vector space over the field of real numbers in which one-dimensional linear subspaces are considered as &ldquo;points&rdquo; and two-dimensional linear subspaces are considered as &ldquo;lines&rdquo;. Equivalently, a sphere in which pairs of antipodal points are considered as &ldquo;points&rdquo; and great circles are considered as &ldquo;lines&rdquo;.