proposition: Lemma fcatCA (s1 s2 s3 : fmap) : [&& disj s1 s2, disj s2 s3 & disj s1 s3] -> fcat (fcat s1 s2) s3 = fcat (fcat s1 s3) s2.
proof: Proof. by case/and3P=>H1 H2 H3; rewrite !fcatA // ?(@fcatC s2 s3) ?(disjC s3). Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path) pcm(options)