$\forall$$T$:Type, $P$:($T$$\rightarrow\mathbb{B}$), $L$, $L_{1}$, $L_{2}$:$T$ List.
\\[0ex]interleaving($T$;$L_{1}$;$L_{2}$;$L$) $\Rightarrow$ interleaving($T$;filter($P$;$L_{1}$);filter($P$;$L_{2}$);filter($P$;$L$))