Trivial Subgroup is Normal

Theorem
Let $\struct {G, \circ}$ be a group whose identity is $e$.

Then the trivial subgroup $\struct {\set e, \circ}$ of $G$ is a normal subgroup in $G$.

Proof
First, by Trivial Subgroup is Subgroup, $\struct {\set e, \circ}$ is a subgroup of $G$.

To show $\struct {\set e, \circ}$ is normal in $G$:


 * $\forall a \in G: a \circ e \circ a^{-1} = a \circ a^{-1} = e$

Hence the result.