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Ultralimit :''For the direct limit of a sequence of ultrapowers, see Ultraproduct.'' In mathematics, an ultralimit is a geometric construction that assigns to a sequence of metric spaces ''Xn'' a limiting metric space. The notion of an ultralimit captures the limiting behavior of finite configurations in the spaces ''Xn'' and uses an ultrafilter to avoid the process of repeatedly passing to subsequences to ensure convergence. An ultralimit is a generalization of the notion of Gromov-Hausdorff convergence of metric spaces. ==Ultrafilters==
Recall that an ultrafilter ''ω'' on the set of natural numbers is a finite-additive set function (which can be thought of as a measure) from the power set (that is, the set of ''all'' subsets of ) to the set such that . An ultrafilter ''ω'' on is ''non-principal'' if for every finite subset we have ''ω''(''F'')=0.
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「Ultralimit」の詳細全文を読む
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