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Essential manifold a special type of closed manifolds. The notion was first introduced explicitly by Mikhail Gromov.〔Gromov, M.: Filling Riemannian manifolds, J. Diff. Geom. 18 (1983), 1–147.〕 ==Definition== A closed manifold ''M'' is called essential if its fundamental class () defines a nonzero element in the homology of its fundamental group ''π'', or more precisely in the homology of the corresponding Eilenberg–MacLane space ''K''(''π'', 1), via the natural homomorphism :, where ''n'' is the dimension of ''M''. Here the fundamental class is taken in homology with integer coefficients if the manifold is orientable, and in coefficients modulo 2, otherwise. 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「essential manifold」の詳細全文を読む スポンサード リンク
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