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In geometry, Boy's surface is an immersion of the real projective plane in 3-dimensional space found by Werner Boy in 1901 (he discovered it on assignment from David Hilbert to prove that the projective plane ''could not'' be immersed in 3-space). Unlike the Roman surface and the cross-cap, it has no singularities (i.e., pinch-points), but it does self-intersect. Boy's surface is discussed (and illustrated) in Jean-Pierre Petit's ''Le Topologicon''.〔(Jean-Pierre Petit, ''Le Topologicon'' )〕 Boy's surface was first parametrized explicitly by Bernard Morin in 1978. See below for another parametrization, discovered by Rob Kusner and Robert Bryant. Boy's surface is one of the two possible immersions of the real projective plane which have only a single triple point. ==Construction== To make a Boy's surface: #Start with a sphere. Remove a cap. #Attach one end of each of three strips to alternate sixths of the edge left by removing the cap. #Bend each strip and attach the other end of each strip to the sixth opposite the first end, so that the inside of the sphere at one end is connected to the outside at the other. Make the strips skirt the middle rather than go through it. #Join the loose edges of the strips. The joins intersect the strips. 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「Boy's surface」の詳細全文を読む スポンサード リンク
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