$\forall$$T$:Type, $L_{1}$, $L_{2}$, $L$:$T$ List. disjoint\_sublists($T$;$L_{1}$;$L_{2}$;$L$) $\Rightarrow$ $\parallel$$L_{1}$$\parallel$+$\parallel$$L_{2}$$\parallel\leq\parallel$$L$$\parallel$