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In mathematics, a topological group ''G'' is called the topological direct sum〔E. Hewitt and K. A. Ross, Abstract harmonic analysis. Vol. I, second edition, Grundlehren der Mathematischen Wissenschaften, 115, Springer, Berlin, 1979. MR0551496 (81k:43001)〕 of two subgroups ''H''1 and ''H''2 if the map : is a topological isomorphism. More generally, ''G'' is called the direct sum of a finite set of subgroups of the map : Note that if a topological group ''G'' is the topological direct sum of the family of subgroups then in particular, as an abstract group (without topology) it is also the direct sum (in the usual way) of the family . ==Topological direct summands== Given a topological group ''G'', we say that a subgroup ''H'' is a topological direct summand of ''G'' (or that splits topologically form ''G'' ) if and only if there exist another subgroup ''K'' ≤ ''G'' such that ''G'' is the direct sum of the subgroups ''H'' and ''K''. A the subgroup ''H'' is a topological direct summand if and only if the extension of topological groups : splits, where is the natural inclusion and is the natural projection. 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「Direct sum of topological groups」の詳細全文を読む スポンサード リンク
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