Symmetric Group is Subgroup of Monoid of Self-Maps
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Theorem
Let $S$ be a set.
Let $S^S$ be the set of all mappings from $S$ to itself
Let $\struct {\Gamma \paren S, \circ}$ denote the symmetric group on $S$.
Let $\struct {S^S, \circ}$ be the monoid of self-maps under composition of mappings.
Then $\struct {\Gamma \paren S, \circ}$ is a subgroup of $\struct {S^S, \circ}$.
Proof
By Symmetric Group is Group, $\struct {\Gamma \paren S, \circ}$ is a group.
Let $\phi \in \Gamma \paren S$ be a permutation on $S$.
As a permutation is a self-map, it follows that $\phi \in S^S$.
Thus by definition $\Gamma \paren S$ is a subset of $S^S$.
So by definition, $\Gamma \paren S$, is a subgroup of $\struct {S^S, \circ}$.
$\blacksquare$