Let τ be a fixed odd permutation in . S₁₀ Show that every odd permutation in S₁₀ is
a product of τ and some permutation in A₁₀
Solution:
Proof. Let be an odd permutation in . We must show that there exists an even permutation such that . Indeed, we may take , since as the product of two odd permutations, it is an even permutation, and
For completeness, let's prove directly that is even. From the definition of an odd permutation, there exist a finite number of transpositions for some odd such that
Similarly, since is also an odd permutation, there exist a finite number of transpositions for some odd such that . Consider now the permutation
I claim that this lies in . Indeed we have
The sum of two odd numbers is even, and so it follows that this is an even permutation.
Thus, if we take , we can prove it same way.
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