$\forall$$T$:Type, $n$, $m$:$\mathbb{N}$, $f$:($T$$\rightarrow$$T$). $f$$^{\mbox{\scriptsize $n$+$m$}}$ = ($f$$^{\mbox{\scriptsize $n$}}$ o $f$$^{\mbox{\scriptsize $m$}}$) $\in$ $T$$\rightarrow$$T$