proposition: Lemma i63lt_le_succ (x y : i63) : x < y -> x + 1 <= y.
proof: Proof. intros equ. assert (i63add_safe x 1). { apply i63add_unwrap. + intros F; discriminate. + unfold i63le, i63lt in *. rewrite i63sub_max_safe. ++ change (to_Z 1) with 1%Z. assert (to_Z y <= to_Z max_i63)%Z by apply i63le_max_int. lia. ++ intro F; discriminate. } unfold i63le, i63lt in *. rewrite H. change (to_Z 1) with 1%Z. lia. Qed.
imports: Coq(RelationClasses ZArith Int63 Lia)