$\forall$$T$:Type, ${\it op}$:($T$$\rightarrow$$T$$\rightarrow$$T$), ${\it id}$:$T$, ${\it inv}$:($T$$\rightarrow$$T$). Inverse($T$;${\it op}$;${\it id}$;${\it inv}$) $\in$ $\mathbb{P}$