proposition: Lemma cardfs_eq0 A : (#|` A| == 0) = (A == fset0).
proof: Proof. by rewrite -(@card_fsub A) // cards_eq0 fsub_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)