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In mathematics, a double cover or double covering may refer to: *Double cover (topology), a two-to-one mapping from one topological space to another. Frequently occurring special cases include * *The orientable double cover of a non-orientable manifold * *The bipartite double cover of an undirected graph ''G'', formed by the graph tensor product ''G'' ×''K''2 * *A double covering group of a topological group such as a Lie group, a group extension of index two formed by a topological double cover. A double cover may also be used to refer to non-topological group extensions of index two, for instance extensions of finite groups. *Cycle double cover, a collection of cycles in a graph that together include each edge twice. The cycle double cover conjecture is the unproven assertion that every bridgeless graph has a cycle double cover. Double coverage may also refer to: *Double coverage, a defensive strategy in American football, basketball, and other sports *Being covered by more than one health insurance plan *A type of Asphalt roll roofing. 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「double cover」の詳細全文を読む スポンサード リンク
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