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<math>\sigma \beta </math> = even | <math>\sigma \beta </math> = even | ||
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| + | Different <math> \beta </math> give different <math>\sigma \beta </math>. Thus there are as many even permutations as there are odd ones. | ||
Revision as of 14:26, 9 September 2008
Question: Show that if H is a subgroup of $ S_n $, then either every member of H is an even permutation or exactly half of the members are even.
Answer: Suppose H contains at least one odd permutation, say $ \sigma $. For each odd permutation $ \beta $, the permutation $ \sigma \beta $ is even.
Note:
$ \sigma $ = odd
$ \beta $ = odd
$ \sigma \beta $ = even
Different $ \beta $ give different $ \sigma \beta $. Thus there are as many even permutations as there are odd ones.
