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In mathematics, a quasi-finite field〔 say that the field satisfies "Moriya's axiom"〕 is a generalisation of a finite field. Standard local class field theory usually deals with complete valued fields whose residue field is ''finite'' (i.e. non-archimedean local fields), but the theory applies equally well when the residue field is only assumed quasi-finite.〔As shown by Mikao Moriya 〕 == Formal definition == A quasi-finite field is a perfect field ''K'' together with an isomorphism of topological groups : where ''K''''s'' is an algebraic closure of ''K'' (necessarily separable because ''K'' is perfect). The field extension ''K''''s''/''K'' is infinite, and the Galois group is accordingly given the Krull topology. The group is the profinite completion of integers with respect to its subgroups of finite index. This definition is equivalent to saying that ''K'' has a unique (necessarily cyclic) extension ''K''''n'' of degree ''n'' for each integer ''n'' ≥ 1, and that the union of these extensions is equal to ''K''''s''. Moreover, as part of the structure of the quasi-finite field, there is a generator ''F''''n'' for each Gal(''K''''n''/''K''), and the generators must be ''coherent'', in the sense that if ''n'' divides ''m'', the restriction of ''F''''m'' to ''K''''n'' is equal to ''F''''n''. 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「Quasi-finite field」の詳細全文を読む スポンサード リンク
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