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(************************************************************************)
(* * The Coq Proof Assistant / The Coq 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) *)
(************************************************************************)
(** * Relations over pairs *)
Require Import SetoidList.
Require Import Relations Morphisms.
(* NB: This should be system-wide someday, but for that we need to
fix the simpl tactic, since "simpl fst" would be refused for
the moment.
Arguments fst {A B}.
Arguments snd {A B}.
Arguments pair {A B}.
/NB *)
Local Notation Fst := (@fst _ _).
Local Notation Snd := (@snd _ _).
Arguments relation_conjunction A%type (R R')%signature _ _.
Arguments relation_equivalence A%type (_ _)%signature.
Arguments subrelation A%type (R R')%signature.
Arguments Reflexive A%type R%signature.
Arguments Irreflexive A%type R%signature.
Arguments Symmetric A%type R%signature.
Arguments Transitive A%type R%signature.
Arguments PER A%type R%signature.
Arguments Equivalence A%type R%signature.
Arguments StrictOrder A%type R%signature.
Generalizable Variables A B RA RB Ri Ro f.
(** Any function from [A] to [B] allow to obtain a relation over [A]
out of a relation over [B]. *)
Definition RelCompFun {A} {B : Type}(R:relation B)(f:A->B) : relation A :=
fun a a' => R (f a) (f a').
(** Instances on RelCompFun must match syntactically *)
Global Typeclasses Opaque RelCompFun.
Infix "@@" := RelCompFun (at level 30, right associativity) : signature_scope.
Notation "R @@1" := (R @@ Fst)%signature (at level 30) : signature_scope.
Notation "R @@2" := (R @@ Snd)%signature (at level 30) : signature_scope.
(** We declare measures to the system using the [Measure] class.
Otherwise the instances would easily introduce loops,
never instantiating the [f] function. *)
Class Measure {A B} (f : A -> B).
(** Standard measures. *)
#[global]
Instance fst_measure {A B} : @Measure (A * B) A Fst := {}.
#[global]
Instance snd_measure {A B} : @Measure (A * B) B Snd := {}.
(** We define a product relation over [A*B]: each components should
satisfy the corresponding initial relation. *)
Definition RelProd {A : Type} {B : Type} (RA:relation A)(RB:relation B) : relation (A*B) :=
relation_conjunction (@RelCompFun (A * B) A RA fst) (RB @@2).
Global Typeclasses Opaque RelProd.
Infix "*" := RelProd : signature_scope.
Section RelCompFun_Instances.
Context {A : Type} {B : Type} (R : relation B).
Global Instance RelCompFun_Reflexive
`(Measure A B f, Reflexive _ R) : Reflexive (R@@f).
Proof. firstorder. Qed.
Global Instance RelCompFun_Symmetric
`(Measure A B f, Symmetric _ R) : Symmetric (R@@f).
Proof. firstorder. Qed.
Global Instance RelCompFun_Transitive
`(Measure A B f, Transitive _ R) : Transitive (R@@f).
Proof. firstorder. Qed.
Global Instance RelCompFun_Irreflexive
`(Measure A B f, Irreflexive _ R) : Irreflexive (R@@f).
Proof. firstorder. Qed.
Global Instance RelCompFun_Equivalence
`(Measure A B f, Equivalence _ R) : Equivalence (R@@f) := {}.
Global Instance RelCompFun_StrictOrder
`(Measure A B f, StrictOrder _ R) : StrictOrder (R@@f) := {}.
End RelCompFun_Instances.
Section RelProd_Instances.
Context {A : Type} {B : Type} (RA : relation A) (RB : relation B).
Global Instance RelProd_Reflexive `(Reflexive _ RA, Reflexive _ RB) : Reflexive (RA*RB).
Proof. firstorder. Qed.
Global Instance RelProd_Symmetric `(Symmetric _ RA, Symmetric _ RB)
: Symmetric (RA*RB).
Proof. firstorder. Qed.
Global Instance RelProd_Transitive
`(Transitive _ RA, Transitive _ RB) : Transitive (RA*RB).
Proof. firstorder. Qed.
Global Program Instance RelProd_Equivalence
`(Equivalence _ RA, Equivalence _ RB) : Equivalence (RA*RB).
Lemma FstRel_ProdRel :
relation_equivalence (RA @@1) (RA*(fun _ _ : B => True)).
Proof. firstorder. Qed.
Lemma SndRel_ProdRel :
relation_equivalence (RB @@2) ((fun _ _ : A =>True) * RB).
Proof. firstorder. Qed.
Global Instance FstRel_sub :
subrelation (RA*RB) (RA @@1).
Proof. firstorder. Qed.
Global Instance SndRel_sub :
subrelation (RA*RB) (RB @@2).
Proof. firstorder. Qed.
Global Instance pair_compat :
Proper (RA==>RB==> RA*RB) (@pair _ _).
Proof. firstorder. Qed.
Global Instance fst_compat :
Proper (RA*RB ==> RA) Fst.
Proof.
intros (x,y) (x',y') (Hx,Hy); compute in *; auto.
Qed.
Global Instance snd_compat :
Proper (RA*RB ==> RB) Snd.
Proof.
intros (x,y) (x',y') (Hx,Hy); compute in *; auto.
Qed.
Global Instance RelCompFun_compat (f:A->B)
`(Proper _ (Ri==>Ri==>Ro) RB) :
Proper (Ri@@f==>Ri@@f==>Ro) (RB@@f)%signature.
Proof. unfold RelCompFun; firstorder. Qed.
End RelProd_Instances.
#[global]
Hint Unfold RelProd RelCompFun : core.
#[global]
Hint Extern 2 (RelProd _ _ _ _) => split : core.
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