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In mathematics, in the topology of 3-manifolds, the sphere theorem of gives conditions for elements of the second homotopy group of a 3-manifold to be represented by embedded spheres. One example is the following: Let be an orientable 3-manifold such that is not the trivial group. Then there exists a non-zero element of having a representative that is an embedding . The proof of this version can be based on transversality methods, see Batude below. Another more general version (also called the projective plane theorem due to Epstein) is: Let be any 3-manifold and a -invariant subgroup of . If is a general position map such that and is any neighborhood of the singular set , then there is a map satisfying #, #, # is a covering map, and # is a 2-sided submanifold (2-sphere or projective plane) of . quoted in Hempel (p. 54) ==References== * * * * * 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「Sphere theorem (3-manifolds)」の詳細全文を読む スポンサード リンク
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