proposition: Lemma zunit_disj f1 f2 : disj f1 f2 = disj (zip_unit f1) (zip_unit f2).
proof: Proof. case: disjP; case: disjP=>//; rewrite !zunit_supp. - by move=>x H1 H2; move/(_ _ H1); rewrite H2. by move=>H x; move/H/negbTE=>->. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path) pcm(options)