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In topology, a branch of mathematics, local flatness is a property of a submanifold in a topological manifold of larger dimension. In the category of topological manifolds, locally flat submanifolds play a role similar to that of embedded submanifolds in the category of smooth manifolds. Suppose a ''d'' dimensional manifold ''N'' is embedded into an ''n'' dimensional manifold ''M'' (where ''d'' < ''n''). If we say ''N'' is locally flat at ''x'' if there is a neighborhood of ''x'' such that the topological pair is homeomorphic to the pair , with a standard inclusion of as a subspace of . That is, there exists a homeomorphism such that the image of coincides with . The above definition assumes that, if ''M'' has a boundary, ''x'' is not a boundary point of ''M''. If ''x'' is a point on the boundary of ''M'' then the definition is modified as follows. We say that ''N'' is locally flat at a boundary point ''x'' of ''M'' if there is a neighborhood of ''x'' such that the topological pair is homeomorphic to the pair , where is a standard half-space and is included as a standard subspace of its boundary. In more detail, we can set and . We call ''N'' locally flat in ''M'' if ''N'' is locally flat at every point. Similarly, a map is called locally flat, even if it is not an embedding, if every ''x'' in ''N'' has a neighborhood ''U'' whose image is locally flat in ''M''. Local flatness of an embedding implies strong properties not shared by all embeddings. Brown (1962) proved that if ''d'' = ''n'' − 1, then ''N'' is collared; that is, it has a neighborhood which is homeomorphic to ''N'' × () with ''N'' itself corresponding to ''N'' × 1/2 (if ''N'' is in the interior of ''M'') or ''N'' × 0 (if ''N'' is in the boundary of ''M''). ==See also== *Neat submanifold 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「local flatness」の詳細全文を読む スポンサード リンク
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