\begin{definition}[Definition:Permutable Subgroups]
Let $\struct {G, \circ}$ be a group.
Let $H$ and $K$ be subgroups of $G$.
Let $H \circ K$ denote the subset product of $H$ and $K$.
Then $H$ and $K$ are '''permutable''' {{iff}}:
:$H \circ K = K \circ H$
\end{definition}