nLab alternating group

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An alternating group $A_n$ is a subgroup of a symmetric group $S_n$ consisting of the even permutations.

The alternating group $A_n$ is to the symmetric group $S_n$ as the special orthogonal group $SO(n)$ is to the orthogonal group $O(n)$ . See also at symmetric group – Whitehead tower

The alternating group $A_4$ on four elements is isomorphic to the orientation-preserving tetrahedral group.
The alternating group $A_5$ on five elements, of order $60$ , is the smallest nonabelian simple group. Geometrically, it may be realized as finite subgroup of SO(3) which carries a regular icosahedron into itself: the icosahedral group.
For all $n \geq 5$ , the alternating group $A_n$ is simple. This is true even if $n$ is infinite: define $Alt(X)$ for any set $X$ to consist of all permutations of $X$ each of which fixes all but finitely elements, and which is an even permutation on that finite subset.

Last revised on September 11, 2018 at 18:34:46. See the history of this page for a list of all contributions to it.