proposition: Lemma disjoint_catfCA f g h : [disjoint domf f & domf g]%fmap -> f + (g + h) = g + (f + h).
proof: Proof. by move=> dfg; rewrite catfCA remf_id. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)