Symmetric group
Not to be confused with Symmetry group
Definition The symmetric group Sn on a finite set of
n symbols is the group
whose elements are all the permutations of the n symbols,
and whose group operation
is the composition of such permutations.
Since there are n! possible permutations of a set of n symbols,
it follows that |Sn| = n!
(symmetric groups can be defined on infinite sets as well, they
behave quite differently).