Definition:Closed under Inversion

Definition
Let $\struct {G, \circ}$ be an group with an identity element $e$.

Let $H \subseteq G$ be a subset of $G$.

Then $H$ is closed under inversion :


 * $\forall h \in H: h^{-1} \in H$

That is, the inverse of every element of $H$ is itself in $H$.