proposition: Lemma fproper_ltn_card A B : A `<` B -> (#|` A| < #|` B|)%N.
proof: Proof. by rewrite fproperEcard => /andP []. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)