$\forall$$T$:Type, ${\it eq}$:($T$$\rightarrow$$T$$\rightarrow\mathbb{B}$), $f$:($\mathbb{N}\rightarrow$$T$), $x$:$T$, $p$:$\mathbb{N}$, $q$:$\mathbb{N}^{+}$. frequency($f$;$x$) $\sim$ ($p$/$q$) $\in$ $\mathbb{P}$