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誰負(fù)韶華新蟲 (小有名氣)
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[求助]
兩道證群不同構(gòu)的題,求解!
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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,表示這一類證明不同構(gòu)的題不怎么會!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 ] |
新蟲 (小有名氣)
木蟲 (初入文壇)
至尊木蟲 (著名寫手)
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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. |

新蟲 (小有名氣)
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