$\forall$$T$:Type, $R$:($T$$\rightarrow$$T$$\rightarrow\mathbb{P}$).
\\[0ex]sum\_of\_torder($T$;$R$) $\Rightarrow$ ($\forall$$x$, $y$, ${\it x'}$, ${\it y'}$:$T$. ($R$($x$,$y$)) $\Rightarrow$ ($R$!(${\it y'}$,$y$)) $\Rightarrow$ (($R$($x$,${\it y'}$)) $\vee$ ($x$ = ${\it y'}$)))