$\forall$$T$:Type, $R_{1}$, $R_{2}$:($T$$\rightarrow$$T$$\rightarrow\mathbb{P}$). $R_{1}$ $\Leftarrow\!\Rightarrow$ $R_{2}$ $\Rightarrow$ $R_{2}$ $\Leftarrow\!\Rightarrow$ $R_{1}$