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In abstract algebra, a Kummer ring is a subring of the ring of complex numbers, such that each of its elements has the form : where ζ is an ''m''th root of unity, i.e. : and ''n''0 through ''n''''m''−1 are integers. A Kummer ring is an extension of , the ring of integers, hence the symbol . Since the minimal polynomial of ζ is the ''m''th cyclotomic polynomial, the ring is an extension of degree (where φ denotes Euler's totient function). An attempt to visualize a Kummer ring on an Argand diagram might yield something resembling a quaint Renaissance map with compass roses and rhumb lines. The set of units of a Kummer ring contains . By Dirichlet's unit theorem, there are also units of infinite order, except in the cases , (in which case we have the ordinary ring of integers), the case (the Gaussian integers) and the cases , (the Eisenstein integers). Kummer rings are named after Ernst Kummer, who studied the unique factorization of their elements. ==See also== * Kummer theory 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「Kummer ring」の詳細全文を読む スポンサード リンク
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