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誰(shuí)負(fù)韶華新蟲(chóng) (小有名氣)
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[求助]
兩道證群不同構(gòu)的題,求解啊!
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1.Prove that An×Z2 is not isomorphic to Sn when n≥3. 2.Show that SOn×Z2 is not isomorphic to On when n is even. 最近看近代,表示這一類(lèi)證明不同構(gòu)的題不怎么會(huì)!求指導(dǎo),最好是英文版的解答!多謝了! [ 發(fā)自手機(jī)版 http://www.gaoyang168.com/3g ] |
至尊木蟲(chóng) (著名寫(xiě)手)
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you may use the information of center group to prove the first. It is known that Sn only has trivial center (when n>=3), this you can see from the conjugation action on the generating set (1k) k=2,...,n. (1k)^phi = (1^phi k^phi). but An X Z2 has nontrivial center, at least Z2 is in the center. (when n=3, the whole group is abelian). So no isomorphism. O_n (when n is even) has center I and -I. (you need to prove this, though I cannot come up a simple proof). but both these two elements belong to SOn. Therefore if On is isomorphic to SOn X Z2, then its center is at least (I, -I) X Z2, has four elements. which is not true. |

木蟲(chóng) (初入文壇)
新蟲(chóng) (小有名氣)
新蟲(chóng) (小有名氣)
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