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