proposition: Lemma fdisjointXU A B C : [disjoint A & B `|` C] = [disjoint A & B]%fset && [disjoint A & C]%fset.
proof: Proof. by rewrite -!fsetI_eq0 fsetIUr fsetU_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)