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In algebra, the integral closure of an ideal ''I'' of a commutative ring ''R'', denoted by , is the set of all elements ''r'' in ''R'' that are integral over ''I'': there exist such that : It is similar to the integral closure of a subring. For example, if ''R'' is a domain, an element ''r'' in ''R'' belongs to if and only if there is a finitely generated ''R''-module ''M'', annihilated only by zero, such that . It follows that is an ideal of ''R'' (in fact, the integral closure of an ideal is always an ideal; see below.) ''I'' is said to be integrally closed if . The integral closure of an ideal appears in a theorem of Rees that characterizes an analytically unramified ring. == Examples == *In , is integral over . *Radical ideals (e.g., prime ideals) are integrally closed. The intersection of integrally closed ideals is integrally closed. *Let be a polynomial ring over a field ''k''. An ideal ''I'' in ''R'' is called monomial if it is generated by monomials; i.e., . The integral closure of a monomial ideal is monomial. 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「Integral closure of an ideal」の詳細全文を読む スポンサード リンク
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