proposition: Theorem spec_eqb x y : eqb x y = Z.eqb (to_Z x) (to_Z y).
proof: Proof. apply Bool.eq_iff_eq_true. unfold eqb. rewrite Z.eqb_eq, <- Z.compare_eq_iff, spec_compare. split; [now destruct Z.compare | now intros ->]. Qed.
imports: ZArith Lia BigNumPrelude NSig ZSig