proposition: Lemma cards0_eq A : #|A| = 0 -> A = set0.
proof: Proof. by move=> A_0; apply/setP=> x; rewrite inE (card0_eq A_0). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)