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+Require Import NumPrelude.
+Require Import ZDomain.
+
+Module Type IntSignature.
+Declare Module Export DomainModule : DomainSignature.
+
+Parameter Inline O : Z.
+Parameter Inline S : Z -> Z.
+Parameter Inline P : Z -> Z.
+
+Notation "0" := O.
+
+Add Morphism S with signature E ==> E as S_wd.
+Add Morphism P with signature E ==> E as P_wd.
+
+Axiom S_inj : forall x y : Z, S x == S y -> x == y.
+Axiom S_P : forall x : Z, S (P x) == x.
+
+Axiom induction :
+  forall Q : Z -> Prop,
+    pred_wd E Q -> Q 0 ->
+    (forall x, Q x -> Q (S x)) ->
+    (forall x, Q x -> Q (P x)) -> forall x, Q x.
+
+End IntSignature.
+
+
+Module IntProperties (Export IntModule : IntSignature).
+
+Module Export DomainPropertiesModule := DomainProperties DomainModule.
+
+Ltac induct n :=
+  try intros until n;
+  pattern n; apply induction; clear n;
+  [unfold NumPrelude.pred_wd;
+  let n := fresh "n" in
+  let m := fresh "m" in
+  let H := fresh "H" in intros n m H; qmorphism n m | | |].
+
+Theorem P_inj : forall x y, P x == P y -> x == y.
+Proof.
+intros x y H.
+setoid_replace x with (S (P x)); [| symmetry; apply S_P].
+setoid_replace y with (S (P y)); [| symmetry; apply S_P].
+now rewrite H.
+Qed.
+
+Theorem P_S : forall x, P (S x) == x.
+Proof.
+intro x.
+apply S_inj.
+now rewrite S_P.
+Qed.
+
+(* The following tactics are intended for replacing a certain
+occurrence of a term t in the goal by (S (P t)) or by (P (S t)).
+Unfortunately, this cannot be done by setoid_replace tactic for two
+reasons. First, it seems impossible to do rewriting when one side of
+the equation in question (S_P or P_S) is a variable, due to bug 1604.
+This does not work even when the predicate is an identifier (e.g.,
+when one tries to rewrite (Q x) into (Q (S (P x)))). Second, the
+setoid_rewrite tactic, like the ordinary rewrite tactic, does not
+allow specifying the exact occurrence of the term to be rewritten. Now
+while not in the setoid context, this occurrence can be specified
+using the pattern tactic, it does not work with setoids, since pattern
+creates a lambda abstractuion, and setoid_rewrite does not work with
+them. *)
+
+Ltac rewrite_SP t set_tac repl thm :=
+let x := fresh "x" in
+set_tac x t;
+setoid_replace x with (repl x); [| symmetry; apply thm];
+unfold x; clear x.
+
+Tactic Notation "rewrite_S_P" constr(t) :=
+rewrite_SP t ltac:(fun x t => (set (x := t))) (fun x => (S (P x))) S_P.
+
+Tactic Notation "rewrite_S_P" constr(t) "at" integer(k) :=
+rewrite_SP t ltac:(fun x t => (set (x := t) in |-* at k)) (fun x => (S (P x))) S_P.
+
+Tactic Notation "rewrite_P_S" constr(t) :=
+rewrite_SP t ltac:(fun x t => (set (x := t))) (fun x => (P (S x))) P_S.
+
+Tactic Notation "rewrite_P_S" constr(t) "at" integer(k) :=
+rewrite_SP t ltac:(fun x t => (set (x := t) in |-* at k)) (fun x => (P (S x))) P_S.
+
+(* One can add tactic notations for replacements in assumptions rather
+than in the goal. For the reason of many possible variants, the core
+of the tactic is factored out. *)
+
+Section Induction.
+
+Variable Q : Z -> Prop.
+Hypothesis Q_wd : pred_wd E Q.
+
+Add Morphism Q with signature E ==> iff as Q_morph.
+Proof Q_wd.
+
+Theorem induction_n :
+  forall n, Q n ->
+    (forall m, Q m -> Q (S m)) ->
+    (forall m, Q m -> Q (P m)) -> forall m, Q m.
+Proof.
+induct n.
+intros; now apply induction.
+intros n IH H1 H2 H3; apply IH; try assumption. apply H3 in H1; now rewrite P_S in H1.
+intros n IH H1 H2 H3; apply IH; try assumption. apply H2 in H1; now rewrite S_P in H1.
+Qed.
+
+End Induction.
+
+Ltac induct_n k n :=
+  try intros until k;
+  pattern k; apply induction_n with (n := n); clear k;
+  [unfold NumPrelude.pred_wd;
+  let n := fresh "n" in
+  let m := fresh "m" in
+  let H := fresh "H" in intros n m H; qmorphism n m | | |].
+
+End IntProperties.