# Library Coq.ZArith.Int

# An light axiomatization of integers (used in FSetAVL).

We define a signature for an integer datatype based on Z. The goal is to allow a switch after extraction to ocaml's big_int or even int when finiteness isn't a problem (typically : when mesuring the height of an AVL tree).
Require Import ZArith.
Delimit Scope Int_scope with I.
Local Open Scope Int_scope.

# a specification of integers

Module Type Int.
Parameter t : Set.
Parameter i2z : t -> Z.
Parameter _0 : t.
Parameter _1 : t.
Parameter _2 : t.
Parameter _3 : t.
Parameter plus : t -> t -> t.
Parameter opp : t -> t.
Parameter minus : t -> t -> t.
Parameter mult : t -> t -> t.
Parameter max : t -> t -> t.
Notation "0" := _0 : Int_scope.
Notation "1" := _1 : Int_scope.
Notation "2" := _2 : Int_scope.
Notation "3" := _3 : Int_scope.
Infix "+" := plus : Int_scope.
Infix "-" := minus : Int_scope.
Infix "*" := mult : Int_scope.
Notation "- x" := (opp x) : Int_scope.
For logical relations, we can rely on their counterparts in Z, since they don't appear after extraction. Moreover, using tactics like omega is easier this way.
Notation "x == y" := (i2z x = i2z y)
(at level 70, y at next level, no associativity) : Int_scope.
Notation "x <= y" := (i2z x <= i2z y)%Z : Int_scope.
Notation "x < y" := (i2z x < i2z y)%Z : Int_scope.
Notation "x >= y" := (i2z x >= i2z y)%Z : Int_scope.
Notation "x > y" := (i2z x > i2z y)%Z : Int_scope.
Notation "x <= y <= z" := (x <= y /\ y <= z) : Int_scope.
Notation "x <= y < z" := (x <= y /\ y < z) : Int_scope.
Notation "x < y < z" := (x < y /\ y < z) : Int_scope.
Notation "x < y <= z" := (x < y /\ y <= z) : Int_scope.
Some decidability fonctions (informative).
Axiom gt_le_dec : forall x y : t, {x > y} + {x <= y}.
Axiom ge_lt_dec : forall x y : t, {x >= y} + {x < y}.
Axiom eq_dec : forall x y : t, { x == y } + {~ x==y }.
Specifications
First, we ask i2z to be injective. Said otherwise, our ad-hoc equality == and the generic = are in fact equivalent. We define == nonetheless since the translation to Z for using automatic tactic is easier.
Axiom i2z_eq : forall n p : t, n == p -> n = p.
Then, we express the specifications of the above parameters using their Z counterparts.
Axiom i2z_0 : i2z _0 = 0%Z.
Axiom i2z_1 : i2z _1 = 1%Z.
Axiom i2z_2 : i2z _2 = 2%Z.
Axiom i2z_3 : i2z _3 = 3%Z.
Axiom i2z_plus : forall n p, i2z (n + p) = (i2z n + i2z p)%Z.
Axiom i2z_opp : forall n, i2z (-n) = (-i2z n)%Z.
Axiom i2z_minus : forall n p, i2z (n - p) = (i2z n - i2z p)%Z.
Axiom i2z_mult : forall n p, i2z (n * p) = (i2z n * i2z p)%Z.
Axiom i2z_max : forall n p, i2z (max n p) = Z.max (i2z n) (i2z p).
End Int.

# Facts and tactics using Int

Module MoreInt (Import I:Int).
Local Notation int := I.t.
A magic (but costly) tactic that goes from int back to the Z friendly world ...
Hint Rewrite ->
i2z_0 i2z_1 i2z_2 i2z_3 i2z_plus i2z_opp i2z_minus i2z_mult i2z_max : i2z.
Ltac i2z := match goal with
| H : ?a = ?b |- _ =>
generalize (f_equal i2z H);
try autorewrite with i2z; clear H; intro H; i2z
| |- ?a = ?b =>
apply (i2z_eq a b); try autorewrite with i2z; i2z
| H : _ |- _ => progress autorewrite with i2z in H; i2z
| _ => try autorewrite with i2z
end.
A reflexive version of the i2z tactic
this i2z_refl is actually weaker than i2z. For instance, if a i2z is buried deep inside a subterm, i2z_refl may miss it. See also the limitation about Set or Type part below. Anyhow, i2z_refl is enough for applying romega.
Ltac i2z_gen := match goal with
| |- ?a = ?b => apply (i2z_eq a b); i2z_gen
| H : ?a = ?b |- _ =>
generalize (f_equal i2z H); clear H; i2z_gen
| H : eq (A:=Z) ?a ?b |- _ => revert H; i2z_gen
| H : Z.lt ?a ?b |- _ => revert H; i2z_gen
| H : Z.le ?a ?b |- _ => revert H; i2z_gen
| H : Z.gt ?a ?b |- _ => revert H; i2z_gen
| H : Z.ge ?a ?b |- _ => revert H; i2z_gen
| H : _ -> ?X |- _ =>
match type of X with
| Type => clear H; i2z_gen
| Prop => revert H; i2z_gen
end
| H : _ <-> _ |- _ => revert H; i2z_gen
| H : _ /\ _ |- _ => revert H; i2z_gen
| H : _ \/ _ |- _ => revert H; i2z_gen
| H : ~ _ |- _ => revert H; i2z_gen
| _ => idtac
end.
Inductive ExprI : Set :=
| EI0 : ExprI
| EI1 : ExprI
| EI2 : ExprI
| EI3 : ExprI
| EIplus : ExprI -> ExprI -> ExprI
| EIopp : ExprI -> ExprI
| EIminus : ExprI -> ExprI -> ExprI
| EImult : ExprI -> ExprI -> ExprI
| EImax : ExprI -> ExprI -> ExprI
| EIraw : int -> ExprI.
Inductive ExprZ : Set :=
| EZplus : ExprZ -> ExprZ -> ExprZ
| EZopp : ExprZ -> ExprZ
| EZminus : ExprZ -> ExprZ -> ExprZ
| EZmult : ExprZ -> ExprZ -> ExprZ
| EZmax : ExprZ -> ExprZ -> ExprZ
| EZofI : ExprI -> ExprZ
| EZraw : Z -> ExprZ.
Inductive ExprP : Type :=
| EPeq : ExprZ -> ExprZ -> ExprP
| EPlt : ExprZ -> ExprZ -> ExprP
| EPle : ExprZ -> ExprZ -> ExprP
| EPgt : ExprZ -> ExprZ -> ExprP
| EPge : ExprZ -> ExprZ -> ExprP
| EPimpl : ExprP -> ExprP -> ExprP
| EPequiv : ExprP -> ExprP -> ExprP
| EPand : ExprP -> ExprP -> ExprP
| EPor : ExprP -> ExprP -> ExprP
| EPneg : ExprP -> ExprP
| EPraw : Prop -> ExprP.
int to ExprI
Ltac i2ei trm :=
match constr:trm with
| 0 => constr:EI0
| 1 => constr:EI1
| 2 => constr:EI2
| 3 => constr:EI3
| ?x + ?y => let ex := i2ei x with ey := i2ei y in constr:(EIplus ex ey)
| ?x - ?y => let ex := i2ei x with ey := i2ei y in constr:(EIminus ex ey)
| ?x * ?y => let ex := i2ei x with ey := i2ei y in constr:(EImult ex ey)
| max ?x ?y => let ex := i2ei x with ey := i2ei y in constr:(EImax ex ey)
| - ?x => let ex := i2ei x in constr:(EIopp ex)
| ?x => constr:(EIraw x)
end
Z to ExprZ
with z2ez trm :=
match constr:trm with
| (?x + ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EZplus ex ey)
| (?x - ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EZminus ex ey)
| (?x * ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EZmult ex ey)
| (Z.max ?x ?y) => let ex := z2ez x with ey := z2ez y in constr:(EZmax ex ey)
| (- ?x)%Z => let ex := z2ez x in constr:(EZopp ex)
| i2z ?x => let ex := i2ei x in constr:(EZofI ex)
| ?x => constr:(EZraw x)
end.
Prop to ExprP
Ltac p2ep trm :=
match constr:trm with
| (?x <-> ?y) => let ex := p2ep x with ey := p2ep y in constr:(EPequiv ex ey)
| (?x -> ?y) => let ex := p2ep x with ey := p2ep y in constr:(EPimpl ex ey)
| (?x /\ ?y) => let ex := p2ep x with ey := p2ep y in constr:(EPand ex ey)
| (?x \/ ?y) => let ex := p2ep x with ey := p2ep y in constr:(EPor ex ey)
| (~ ?x) => let ex := p2ep x in constr:(EPneg ex)
| (eq (A:=Z) ?x ?y) => let ex := z2ez x with ey := z2ez y in constr:(EPeq ex ey)
| (?x < ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EPlt ex ey)
| (?x <= ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EPle ex ey)
| (?x > ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EPgt ex ey)
| (?x >= ?y)%Z => let ex := z2ez x with ey := z2ez y in constr:(EPge ex ey)
| ?x => constr:(EPraw x)
end.
ExprI to int
Fixpoint ei2i (e:ExprI) : int :=
match e with
| EI0 => 0
| EI1 => 1
| EI2 => 2
| EI3 => 3
| EIplus e1 e2 => (ei2i e1)+(ei2i e2)
| EIminus e1 e2 => (ei2i e1)-(ei2i e2)
| EImult e1 e2 => (ei2i e1)*(ei2i e2)
| EImax e1 e2 => max (ei2i e1) (ei2i e2)
| EIopp e => -(ei2i e)
| EIraw i => i
end.
ExprZ to Z
Fixpoint ez2z (e:ExprZ) : Z :=
match e with
| EZplus e1 e2 => ((ez2z e1)+(ez2z e2))%Z
| EZminus e1 e2 => ((ez2z e1)-(ez2z e2))%Z
| EZmult e1 e2 => ((ez2z e1)*(ez2z e2))%Z
| EZmax e1 e2 => Z.max (ez2z e1) (ez2z e2)
| EZopp e => (-(ez2z e))%Z
| EZofI e => i2z (ei2i e)
| EZraw z => z
end.
ExprP to Prop
Fixpoint ep2p (e:ExprP) : Prop :=
match e with
| EPeq e1 e2 => (ez2z e1) = (ez2z e2)
| EPlt e1 e2 => ((ez2z e1)<(ez2z e2))%Z
| EPle e1 e2 => ((ez2z e1)<=(ez2z e2))%Z
| EPgt e1 e2 => ((ez2z e1)>(ez2z e2))%Z
| EPge e1 e2 => ((ez2z e1)>=(ez2z e2))%Z
| EPimpl e1 e2 => (ep2p e1) -> (ep2p e2)
| EPequiv e1 e2 => (ep2p e1) <-> (ep2p e2)
| EPand e1 e2 => (ep2p e1) /\ (ep2p e2)
| EPor e1 e2 => (ep2p e1) \/ (ep2p e2)
| EPneg e => ~ (ep2p e)
| EPraw p => p
end.
ExprI (supposed under a i2z) to a simplified ExprZ
Fixpoint norm_ei (e:ExprI) : ExprZ :=
match e with
| EI0 => EZraw (0%Z)
| EI1 => EZraw (1%Z)
| EI2 => EZraw (2%Z)
| EI3 => EZraw (3%Z)
| EIplus e1 e2 => EZplus (norm_ei e1) (norm_ei e2)
| EIminus e1 e2 => EZminus (norm_ei e1) (norm_ei e2)
| EImult e1 e2 => EZmult (norm_ei e1) (norm_ei e2)
| EImax e1 e2 => EZmax (norm_ei e1) (norm_ei e2)
| EIopp e => EZopp (norm_ei e)
| EIraw i => EZofI (EIraw i)
end.
ExprZ to a simplified ExprZ
Fixpoint norm_ez (e:ExprZ) : ExprZ :=
match e with
| EZplus e1 e2 => EZplus (norm_ez e1) (norm_ez e2)
| EZminus e1 e2 => EZminus (norm_ez e1) (norm_ez e2)
| EZmult e1 e2 => EZmult (norm_ez e1) (norm_ez e2)
| EZmax e1 e2 => EZmax (norm_ez e1) (norm_ez e2)
| EZopp e => EZopp (norm_ez e)
| EZofI e => norm_ei e
| EZraw z => EZraw z
end.
ExprP to a simplified ExprP
Fixpoint norm_ep (e:ExprP) : ExprP :=
match e with
| EPeq e1 e2 => EPeq (norm_ez e1) (norm_ez e2)
| EPlt e1 e2 => EPlt (norm_ez e1) (norm_ez e2)
| EPle e1 e2 => EPle (norm_ez e1) (norm_ez e2)
| EPgt e1 e2 => EPgt (norm_ez e1) (norm_ez e2)
| EPge e1 e2 => EPge (norm_ez e1) (norm_ez e2)
| EPimpl e1 e2 => EPimpl (norm_ep e1) (norm_ep e2)
| EPequiv e1 e2 => EPequiv (norm_ep e1) (norm_ep e2)
| EPand e1 e2 => EPand (norm_ep e1) (norm_ep e2)
| EPor e1 e2 => EPor (norm_ep e1) (norm_ep e2)
| EPneg e => EPneg (norm_ep e)
| EPraw p => EPraw p
end.
Lemma norm_ei_correct : forall e:ExprI, ez2z (norm_ei e) = i2z (ei2i e).
Lemma norm_ez_correct : forall e:ExprZ, ez2z (norm_ez e) = ez2z e.
Lemma norm_ep_correct :
forall e:ExprP, ep2p (norm_ep e) <-> ep2p e.
Lemma norm_ep_correct2 :
forall e:ExprP, ep2p (norm_ep e) -> ep2p e.
Ltac i2z_refl :=
i2z_gen;
match goal with |- ?t =>
let e := p2ep t in
change (ep2p e); apply norm_ep_correct2; simpl
end.
End MoreInt.

# An implementation of Int

It's always nice to know that our Int interface is realizable :-)
Module Z_as_Int <: Int.
Local Open Scope Z_scope.
Definition t := Z.
Definition _0 := 0.
Definition _1 := 1.
Definition _2 := 2.
Definition _3 := 3.
Definition plus := Z.add.
Definition opp := Z.opp.
Definition minus := Z.sub.
Definition mult := Z.mul.
Definition max := Z.max.
Definition gt_le_dec := Z_gt_le_dec.
Definition ge_lt_dec := Z_ge_lt_dec.
Definition eq_dec := Z.eq_dec.
Definition i2z : t -> Z := fun n => n.
Lemma i2z_eq : forall n p, i2z n=i2z p -> n = p.
Lemma i2z_0 : i2z _0 = 0.
Lemma i2z_1 : i2z _1 = 1.
Lemma i2z_2 : i2z _2 = 2.
Lemma i2z_3 : i2z _3 = 3.
Lemma i2z_plus n p : i2z (n + p) = i2z n + i2z p.
Lemma i2z_opp n : i2z (- n) = - i2z n.
Lemma i2z_minus n p : i2z (n - p) = i2z n - i2z p.
Lemma i2z_mult n p : i2z (n * p) = i2z n * i2z p.
Lemma i2z_max n p : i2z (max n p) = Z.max (i2z n) (i2z p).
End Z_as_Int.