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In the study of metric spaces in mathematics, there are various notions of two metrics on the same underlying space being "the same", or equivalent. In the following, will denote a non-empty set and and will denote two metrics on . ==Topological equivalence== The two metrics and are said to be topologically equivalent if they generate the same topology on . The adjective "topological" is often dropped.〔Bishop and Goldberg, p. 10.〕 There are multiple ways of expressing this condition: * a subset is -open if and only if it is -open; * the open balls "nest": for any point and any radius , there exist radii such that : and * the identity function is both -continuous and -continuous. The following are sufficient but not necessary conditions for topological equivalence: * there exists a strictly increasing, continuous, and subadditive such that .〔Ok, p. 127, footnote 12.〕 * for each , there exist positive constants and such that, for every point , : 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「Equivalence of metrics」の詳細全文を読む スポンサード リンク
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