proposition: Lemma cardfs_gt0 A : (0 < #|` A|)%N = (A != fset0).
proof: Proof. by rewrite lt0n cardfs_eq0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)