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Def: A normal subgroup H of a group G is said to be a direct factor if there exists a (normal)subgroup K of G such that G=H×K problem: (a)If H is a direct factor of K and K is a direct factor of G, then H is normal in G. (b)If H is a direct factor of G,then every homomorphism H → G may be extended to an endomorphism G → G. However,a monomorphism H → G need not be extendible to an automorphism G → G. 以上為Hungerford代數的習題 懇請板上高手協助 感謝!!!! -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 111.252.196.205