\begin{definition}[Definition:Commutator/Group]
Let $\struct {G, \circ}$ be a group.
Let $g, h \in G$.
The '''commutator''' of $g$ and $h$ is the operation:
:$\sqbrk {g, h} := g^{-1} \circ h^{-1} \circ g \circ h$
\end{definition}