proposition: Lemma fsetUUr A B C : A `|` (B `|` C) = (A `|` B) `|` (A `|` C).
proof: Proof. by rewrite !(fsetUC A) fsetUUl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)