proposition: Lemma eq_card_sub (A : {pred sfT}) : A =i predT -> #|A| = #|[pred x | P x]|.
proof: Proof. exact: eq_card_trans card_sub. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path div)