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In mathematics, a quadratic set is a set of points in a projective plane/space which bears the same essential incidence properties as a quadric (conic section in a projective plane, sphere or cone or hyperboloid in a projective space). == Definition of a quadratic set== Let be a projective space. A non empty subset of is called quadratic set if :(QS1) Any line of intersects in at most 2 points or is contained in . :( is called exterior, tangent and secant line if and respectively.) :(QS2) For any point the union of all tangent lines through is a hyperplane or the entire space . A quadratic set is called non degenerated if for any point set is a hyperplane. The following result is an astonishing statement for finite projective spaces. Theorem(BUEKENHOUT): Let be a ''finite'' projective space of dimension and a non degenerated quadratic set which contains lines. Then: is pappian and is a ''quadric'' with index . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「quadratic set」の詳細全文を読む スポンサード リンク
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