proposition: Lemma inj_card_leq (A B: finType) (f : A -> B) : injective f -> #|A| <= #|B|.
proof: Proof. move => inj_f. by rewrite -[#|A|](card_codom (f := f)) // max_card. Qed.
imports: Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone)