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(*         *      The Rocq Prover / The Rocq Development Team           *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
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Attributes deprecated(since="8.20").
Require Export NumPrelude NZAxioms.
(** In this file, we investigate the shape of domains satisfying the [NZDomainSig] interface. In particular, we define a translation from Peano numbers [nat] into NZ. *)
Local Notation "f ^ n" := (fun x => nat_rect _ x (fun _ => f) n).
#[global]
Instance nat_rect_wd n {A} (R:relation A) :
Proper (R==>(R==>R)==>R) (fun x f => nat_rect (fun _ => _) x (fun _ => f) n).
Module NZDomainProp (Import NZ:NZDomainSig').
Include NZBaseProp NZ.
(** * Relationship between points thanks to [succ] and [pred]. *)
(** For any two points, one is an iterated successor of the other. *)

(** In particular, all points are either iterated successors of [0] or iterated predecessors of [0] (or both). *)
Lemma itersucc0_or_iterpred0 :
forall n, exists p:nat, n == (S^p) 0 \/ n == (P^p) 0.