Does a homomorphic image of even permutations consist of even permutations?
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$A_n$ is the set of products of an even number of transpositions
this is one common definition of $A_n$
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$A_n$ is the set of products of products of two transpositions
just group pairs of transpositions
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$A_n$ is the set of products of 3-cycles
$(12)(23)=(123)$, $(12)(34)=(123)(234)$
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$A_n$ is the set of products of squares
$(123)=(132)^2$ and the square of every permutation is even
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$f$ maps products of squares to products of squares
$f$ is a homomorphism
$f$ maps $A_n$ into $A_n$.