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In algebraic topology, a G-spectrum is a spectrum with an action of a (finite) group. Let ''X'' be a spectrum with an action of a finite group ''G''. The important notion is that of the homotopy fixed point set . There is always : a map from the fixed point spectrum to a homotopy fixed point spectrum (because, by definition, is the mapping spectrum .) Example: acts on the complex ''K''-theory ''KU'' by taking the conjugate bundle of a complex vector bundle. Then , the real ''K''-theory. The cofiber of is called the Tate spectrum of ''X''. == ''G''-Galois extension in the sense of Rognes == This notion is due to J. Rognes . Let ''A'' be an E∞-ring with an action of a finite group ''G'' and ''B'' = ''A''''hG'' its invariant subring. Then ''B'' → ''A'' (the map of ''B''-algebras in E∞-sense) is said to be a ''G-Galois extension'' if the natural map : (which generalizes in the classical setup) is an equivalence. The extension is faithful if the Bousfield classes of ''A'', ''B'' over ''B'' are equivalent. Example: ''KO'' → ''KU'' is a ℤ./2-Galois extension. 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「G-spectrum」の詳細全文を読む スポンサード リンク
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