$\forall$$p$:FinProbSpace, $n$:$\mathbb{N}$, $X$, $Y$, $Z$:RandomVariable($p$;$n$).
\\[0ex]rv{-}disjoint($p$;$n$;$Y$;$X$) $\Rightarrow$ rv{-}disjoint($p$;$n$;$Z$;$X$) $\Rightarrow$ rv{-}disjoint($p$;$n$;$Y$ + $Z$;$X$)