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Hopfian group : ウィキペディア英語版 | Hopfian group In mathematics, a Hopfian group is a group ''G'' for which every epimorphism :''G'' → ''G'' is an isomorphism. Equivalently, a group is Hopfian if and only if it is not isomorphic to any of its proper quotients. A group ''G'' is co-Hopfian if every monomorphism :''G'' → ''G'' is an isomorphism. Equivalently, ''G'' is not isomorphic to any of its proper subgroups. ==Examples of Hopfian groups==
* Every finite group, by an elementary counting argument. * More generally, every polycyclic-by-finite group. * Any finitely-generated free group. * The group Q of rationals. * Any finitely generated residually finite group. * Any torsion-free word-hyperbolic group.
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「Hopfian group」の詳細全文を読む
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