proposition: Lemma natmap_eq {A} (m1 m2 : natmap A) : m1 = m2 ↔ natmap_car m1 = natmap_car m2.
proof: Proof. split; [by intros ->|intros]; destruct m1 as [t1 ?], m2 as [t2 ?]. simplify_eq/=; f_equal; apply proof_irrel. Qed.
imports: stdpp(fin_maps mapset) stdpp(options)