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In mathematics, especially homotopy theory, the mapping cone is a construction of topology, analogous to a quotient space. It is also called the homotopy cofiber, and also notated . ==Definition== Given a map , the mapping cone is defined to be the quotient topological space of with respect to the equivalence relation , on ''X''. Here denotes the unit interval () with its standard topology. Note that some (like May) use the opposite convention, switching 0 and 1. Visually, one takes the cone on ''X'' (the cylinder with one end (the 0 end) identified to a point), and glues the other end onto ''Y'' via the map ''f'' (the identification of the 1 end). Coarsely, one is taking the quotient space by the image of ''X,'' so ''Cf'' "=" ''Y''/''f''(''X''); this is not precisely correct because of point-set issues, but is the philosophy, and is made precise by such results as the homology of a pair and the notion of an ''n''-connected map. The above is the definition for a map of unpointed spaces; for a map of pointed spaces (so ), one also identifies all of ; formally, Thus one end and the "seam" are all identified with 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「Mapping cone (topology)」の詳細全文を読む スポンサード リンク
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