$\forall$$T$:Type, $L$:$T$ List, $P$, $Q$:($\mathbb{N}$$_{\mbox{\scriptsize $<\parallel$$L$$\parallel$}}$$\rightarrow$Prop), $R$:($\mathbb{N}$$_{\mbox{\scriptsize $<\parallel$$L$$\parallel$}}$$\rightarrow\mathbb{N}$$_{\mbox{\scriptsize $<\parallel$$L$$\parallel$}}$$\rightarrow$Prop).
\\[0ex]causal\_order($L$;$R$;$P$;$Q$) $\in$ Prop