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In topology, a branch of mathematics, collapse is a concept due to J. H. C. Whitehead.〔Whitehead, J.H.C. (1938) ''Simplical spaces, nuclei and m-groups'', Proceedings of the London Mathematical Society 45, pp 243–327〕 == Definition == Let be an abstract simplicial complex. Suppose that such that the following two conditions are satisfied: (i) , in particular ; (ii) is a maximal face of K and no other maximal face of K contains , then is called a free face. A simplicial collapse of K is the removal of all simplices such that , where is a free face. If additionally we have dim τ = dim σ-1, then this is called an elementary collapse. A simplicial complex that has a sequence of collapses leading to a point is called collapsible. Every collapsible complex is contractible, but the converse is not true. This definition can be extended to CW-complexes and is the basis for the concept of simple-homotopy equivalence.〔Cohen, M.M. (1973) ''A Course in Simple-Homotopy Theory'', Springer-Verlag New York〕 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「Collapse (topology)」の詳細全文を読む スポンサード リンク
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