Library iris.bi.interface

From iris.algebra Require Export ofe.
From iris.bi Require Export notation.
From iris.prelude Require Import options.

Local Set Primitive Projections.

Section bi_mixin.
  Context {PROP : Type} `{!Dist PROP, !Equiv PROP}.
  Context (bi_entails : PROP → PROP → Prop).
  Context (bi_emp : PROP).
  Context (bi_pure : Prop → PROP).
  Context (bi_and : PROP → PROP → PROP).
  Context (bi_or : PROP → PROP → PROP).
  Context (bi_impl : PROP → PROP → PROP).
  Context (bi_forall : ∀ A , (A → PROP ) → PROP).
  Context (bi_exist : ∀ A , (A → PROP ) → PROP).
  Context (bi_sep : PROP → PROP → PROP).
  Context (bi_wand : PROP → PROP → PROP).

  Bind Scope bi_scope with PROP.
  Local Infix "⊢" := bi_entails.
  Local Notation "'emp'" := bi_emp : bi_scope.
  Local Notation "'True'" := (bi_pure True) : bi_scope.
  Local Notation "'False'" := (bi_pure False) : bi_scope.
  Local Notation "'⌜' φ '⌝'" := (bi_pure φ%type%stdpp) : bi_scope.
  Local Infix "∧" := bi_and : bi_scope.
  Local Infix "∨" := bi_or : bi_scope.
  Local Infix "→" := bi_impl : bi_scope.
  Local Notation "∀ x .. y , P" :=
    (bi_forall _ (λ x , .. (bi_forall _ (λ y , P%I)) ..)) : bi_scope.
  Local Notation "∃ x .. y , P" :=
    (bi_exist _ (λ x , .. (bi_exist _ (λ y , P%I)) ..)) : bi_scope.
  Local Infix "∗" := bi_sep : bi_scope.
  Local Infix "-∗" := bi_wand : bi_scope.

Axioms for a general BI (logic of bunched implications)

The following axioms are satisifed by both affine and linear BIs, and BIs that combine both kinds of resources. In particular, we have an "ordered RA" model satisfying all these axioms. For this model, we extend RAs with an arbitrary partial order, and up-close resources wrt. that order (instead of extension order). We demand composition to be monotone wrt. the order: x1 ≼ x2 → x1 ⋅ y ≼ x2 ⋅ y. We define emp := λ r, ε ≼ r; persistently is still defined with the core: persistently P := λ r, P (core r). This is uplcosed because the core is monotone.

  Record BiMixin := {
    bi_mixin_entails_po : PreOrder bi_entails;
    bi_mixin_equiv_entails P Q : (P ≡ Q ) ↔ (P ⊢ Q ) ∧ (Q ⊢ P );

Non-expansiveness

    bi_mixin_pure_ne n : Proper (iff ==> dist n) bi_pure;
    bi_mixin_and_ne : NonExpansive2 bi_and;
    bi_mixin_or_ne : NonExpansive2 bi_or;
    bi_mixin_impl_ne : NonExpansive2 bi_impl;
    bi_mixin_forall_ne A n :
      Proper (pointwise_relation _ (dist n) ==> dist n) (bi_forall A);
    bi_mixin_exist_ne A n :
      Proper (pointwise_relation _ (dist n) ==> dist n) (bi_exist A);
    bi_mixin_sep_ne : NonExpansive2 bi_sep;
    bi_mixin_wand_ne : NonExpansive2 bi_wand;

Higher-order logic

    bi_mixin_pure_intro (φ : Prop) P : φ → P ⊢ ⌜ φ ⌝;
    bi_mixin_pure_elim' (φ : Prop) P : (φ → True ⊢ P ) → ⌜ φ ⌝ ⊢ P;

    bi_mixin_and_elim_l P Q : P ∧ Q ⊢ P;
    bi_mixin_and_elim_r P Q : P ∧ Q ⊢ Q;
    bi_mixin_and_intro P Q R : (P ⊢ Q ) → (P ⊢ R ) → P ⊢ Q ∧ R;

    bi_mixin_or_intro_l P Q : P ⊢ P ∨ Q;
    bi_mixin_or_intro_r P Q : Q ⊢ P ∨ Q;
    bi_mixin_or_elim P Q R : (P ⊢ R ) → (Q ⊢ R ) → P ∨ Q ⊢ R;

    bi_mixin_impl_intro_r P Q R : (P ∧ Q ⊢ R ) → P ⊢ Q → R;
    bi_mixin_impl_elim_l' P Q R : (P ⊢ Q → R ) → P ∧ Q ⊢ R;

    bi_mixin_forall_intro {A} P (Ψ : A → PROP) : (∀ a , P ⊢ Ψ a ) → P ⊢ ∀ a , Ψ a;
    bi_mixin_forall_elim {A} {Ψ : A → PROP} a : (∀ a , Ψ a ) ⊢ Ψ a;

    bi_mixin_exist_intro {A} {Ψ : A → PROP} a : Ψ a ⊢ ∃ a , Ψ a;
    bi_mixin_exist_elim {A} (Φ : A → PROP) Q : (∀ a , Φ a ⊢ Q ) → (∃ a , Φ a ) ⊢ Q;

BI connectives

    bi_mixin_sep_mono P P' Q Q' : (P ⊢ Q ) → (P' ⊢ Q') → P ∗ P' ⊢ Q ∗ Q';
    bi_mixin_emp_sep_1 P : P ⊢ emp ∗ P;
    bi_mixin_emp_sep_2 P : emp ∗ P ⊢ P;
    bi_mixin_sep_comm' P Q : P ∗ Q ⊢ Q ∗ P;
    bi_mixin_sep_assoc' P Q R : (P ∗ Q ) ∗ R ⊢ P ∗ (Q ∗ R );
    bi_mixin_wand_intro_r P Q R : (P ∗ Q ⊢ R ) → P ⊢ Q -∗ R;
    bi_mixin_wand_elim_l' P Q R : (P ⊢ Q -∗ R ) → P ∗ Q ⊢ R;
  }.

We require any BI to have a persistence modality that carves out the intuitionistic fragment of the separation logic. For logics such as Iris, the persistence modality has a non-trivial definition (involving the core of the camera). It is not clear whether a trivial definition exists: while <pers> P := False comes close, it does not satisfy later_persistently_1.

However, for some simpler discrete BIs the persistence modality can be defined as:

<pers> P := ⌜ emp ⊢ P ⌝

That is, P holds persistently if it holds without resources.

The nesting of the entailment below the pure embedding ⌜ ⌝ only works for discrete BIs: Non-expansiveness of <pers> relies on dist ignoring the step-index.

To prove the rule <pers> (∃ a, Ψ a) ⊢ ∃ a, <pers> Ψ a the BI furthermore needs to satisfy the "existential property": emp ⊢ ∃ x, Φ x implies ∃ x, emp ⊢ Φ x.

This construction is formalized by the smart constructor bi_persistently_mixin_discrete for BiPersistentlyMixin. See tests/heapprop and tests/heapprop_affine for examples of how to use this smart constructor.

  Context (bi_persistently : PROP → PROP).
  Local Notation "'<pers>' P" := (bi_persistently P) : bi_scope.

  Record BiPersistentlyMixin := {
    bi_mixin_persistently_ne : NonExpansive bi_persistently;


    bi_mixin_persistently_mono P Q : (P ⊢ Q ) → <pers > P ⊢ <pers > Q;

    bi_mixin_persistently_idemp_2 P : <pers > P ⊢ <pers > <pers > P;


    bi_mixin_persistently_emp_2 : emp ⊢ <pers > emp;


    bi_mixin_persistently_and_2 (P Q : PROP) :
      (<pers > P ) ∧ (<pers > Q ) ⊢ <pers > (P ∧ Q );
    bi_mixin_persistently_exist_1 {A} (Ψ : A → PROP) :
      <pers > (∃ a , Ψ a ) ⊢ ∃ a , <pers > (Ψ a );


    bi_mixin_persistently_absorbing P Q : <pers > P ∗ Q ⊢ <pers > P;

    bi_mixin_persistently_and_sep_elim P Q : <pers > P ∧ Q ⊢ P ∗ Q;
  }.

  Lemma bi_persistently_mixin_discrete :
    (∀ n (P Q : PROP ), P ≡{n }≡ Q → P ≡ Q ) →
    (∀ {A} (Φ : A → PROP ), (emp ⊢ ∃ x , Φ x ) → ∃ x , emp ⊢ Φ x ) →
    (∀ P : PROP , (<pers > P)%I = ⌜ emp ⊢ P ⌝%I) →
    BiMixin →
    BiPersistentlyMixin.
  Proof.
    intros Hdiscrete Hex Hpers Hbi. pose proof (bi_mixin_entails_po Hbi).
    split.
    -
      intros n P Q [HPQ HQP]%Hdiscrete%(bi_mixin_equiv_entails Hbi).
      rewrite !Hpers. apply (bi_mixin_pure_ne Hbi). split⇒ ?; by etrans.
    -
      intros P Q HPQ. rewrite !Hpers. apply (bi_mixin_pure_elim' Hbi)=> ?.
      apply (bi_mixin_pure_intro Hbi). by trans P.
    -
      intros P. rewrite !Hpers. apply (bi_mixin_pure_elim' Hbi)=> ?.
      by do 2 apply (bi_mixin_pure_intro Hbi).
    -
      rewrite Hpers. by apply (bi_mixin_pure_intro Hbi).
    -
      intros P Q. rewrite !Hpers.
      apply (bi_mixin_impl_elim_l' Hbi). apply (bi_mixin_pure_elim' Hbi)=> ?.
      apply (bi_mixin_impl_intro_r Hbi).
      etrans; [apply (bi_mixin_and_elim_r Hbi)|].
      apply (bi_mixin_pure_elim' Hbi)=> ?.
      apply (bi_mixin_pure_intro Hbi). by apply (bi_mixin_and_intro Hbi).
    -
      intros A Φ. rewrite !Hpers. apply (bi_mixin_pure_elim' Hbi)=> /Hex [x ?].
      etrans; [|apply (bi_mixin_exist_intro Hbi x)]; simpl.
      rewrite Hpers. by apply (bi_mixin_pure_intro Hbi).
    -
      intros P Q. rewrite !Hpers.
      apply (bi_mixin_wand_elim_l' Hbi). apply (bi_mixin_pure_elim' Hbi)=> ?.
      apply (bi_mixin_wand_intro_r Hbi). by apply (bi_mixin_pure_intro Hbi).
    -
      intros P Q. rewrite !Hpers.
      apply (bi_mixin_impl_elim_l' Hbi). apply (bi_mixin_pure_elim' Hbi)=> ?.
      apply (bi_mixin_impl_intro_r Hbi).
      etrans; [apply (bi_mixin_and_elim_r Hbi)|].
      etrans; [apply (bi_mixin_emp_sep_1 Hbi)|].
      by apply (bi_mixin_sep_mono Hbi).
  Qed.

We equip any BI with a later modality. This avoids an additional layer in the BI hierarchy and improves performance significantly (see Iris issue 303). For non step-indexed BIs the later modality can simply be defined as the identity function, as the Löb axiom or contractiveness of later is not part of [BiLaterMixin]. For step-indexed BIs one should separately prove an instance of the class [BiLaterContractive PROP] or [BiLöb PROP]. (Note that there is an instance [BiLaterContractive PROP → BiLöb PROP] in [derived_laws_later].) For non step-indexed BIs one can get a "free" instance of [BiLaterMixin] using the smart constructor [bi_later_mixin_id] below.

  Context (bi_later : PROP → PROP).
  Local Notation "▷ P" := (bi_later P) : bi_scope.

  Record BiLaterMixin := {
    bi_mixin_later_ne : NonExpansive bi_later;

    bi_mixin_later_mono P Q : (P ⊢ Q ) → ▷ P ⊢ ▷ Q;
    bi_mixin_later_intro P : P ⊢ ▷ P;

    bi_mixin_later_forall_2 {A} (Φ : A → PROP) : (∀ a , ▷ Φ a ) ⊢ ▷ ∀ a , Φ a;
    bi_mixin_later_exist_false {A} (Φ : A → PROP) :
      (▷ ∃ a , Φ a ) ⊢ ▷ False ∨ (∃ a , ▷ Φ a );
    bi_mixin_later_sep_1 P Q : ▷ (P ∗ Q ) ⊢ ▷ P ∗ ▷ Q;
    bi_mixin_later_sep_2 P Q : ▷ P ∗ ▷ Q ⊢ ▷ (P ∗ Q );
    bi_mixin_later_persistently_1 P : ▷ <pers > P ⊢ <pers > ▷ P;
    bi_mixin_later_persistently_2 P : <pers > ▷ P ⊢ ▷ <pers > P;


    bi_mixin_later_false_em P : ▷ P ⊢ ▷ False ∨ (▷ False → P );
  }.

  Lemma bi_later_mixin_id :
    (∀ (P : PROP ), (▷ P)%I = P ) →
    BiMixin → BiLaterMixin.
  Proof.
    intros Hlater Hbi. pose proof (bi_mixin_entails_po Hbi).
    split; repeat intro; rewrite ?Hlater //.
    - apply (bi_mixin_forall_intro Hbi)=> a.
      etrans; [apply (bi_mixin_forall_elim Hbi a)|]. by rewrite Hlater.
    - etrans; [|apply (bi_mixin_or_intro_r Hbi)].
      apply (bi_mixin_exist_elim Hbi)=> a.
      etrans; [|apply (bi_mixin_exist_intro Hbi a)]. by rewrite /= Hlater.
    - etrans; [|apply (bi_mixin_or_intro_r Hbi)].
      apply (bi_mixin_impl_intro_r Hbi), (bi_mixin_and_elim_l Hbi).
  Qed.
End bi_mixin.

Module Import universes.

The universe of the logic (PROP).

Universe Logic.

The universe of quantifiers in the logic.

  Universe Quant.
End universes.

Structure bi := Bi {
  bi_car :> Type@{Logic};
  bi_dist : Dist bi_car;
  bi_equiv : Equiv bi_car;
  bi_entails : bi_car → bi_car → Prop;
  bi_emp : bi_car;
  bi_pure : Prop → bi_car;
  bi_and : bi_car → bi_car → bi_car;
  bi_or : bi_car → bi_car → bi_car;
  bi_impl : bi_car → bi_car → bi_car;
  bi_forall : ∀ A : Type@{Quant}, (A → bi_car ) → bi_car;
  bi_exist : ∀ A : Type@{Quant}, (A → bi_car ) → bi_car;
  bi_sep : bi_car → bi_car → bi_car;
  bi_wand : bi_car → bi_car → bi_car;
  bi_persistently : bi_car → bi_car;
  bi_later : bi_car → bi_car;
  bi_ofe_mixin : OfeMixin bi_car;
  bi_cofe_aux : Cofe (Ofe bi_car bi_ofe_mixin);
  bi_bi_mixin : BiMixin bi_entails bi_emp bi_pure bi_and bi_or bi_impl bi_forall
                        bi_exist bi_sep bi_wand;
  bi_bi_persistently_mixin :
    BiPersistentlyMixin bi_entails bi_emp bi_and bi_exist bi_sep bi_persistently;
  bi_bi_later_mixin : BiLaterMixin bi_entails bi_pure bi_or bi_impl
                                   bi_forall bi_exist bi_sep bi_persistently bi_later;
}.
Bind Scope bi_scope with bi_car.

Coercion bi_ofeO (PROP : bi) : ofe := Ofe PROP (bi_ofe_mixin PROP).
Canonical Structure bi_ofeO.

The projection bi_cofe_aux is not registered as an instance because it has the wrong type. Its result type is unfolded, i.e., Cofe (Ofe PROP ...), and thus should never be used. The instance bi_cofe has the proper result type Cofe (bi_ofeO PROP).

Global Instance bi_cofe (PROP : bi) : Cofe PROP := bi_cofe_aux PROP.

Global Instance: Params (@bi_entails) 1 := {}.
Global Instance: Params (@bi_emp) 1 := {}.
Global Instance: Params (@bi_pure) 1 := {}.
Global Instance: Params (@bi_and) 1 := {}.
Global Instance: Params (@bi_or) 1 := {}.
Global Instance: Params (@bi_impl) 1 := {}.
Global Instance: Params (@bi_forall) 2 := {}.
Global Instance: Params (@bi_exist) 2 := {}.
Global Instance: Params (@bi_sep) 1 := {}.
Global Instance: Params (@bi_wand) 1 := {}.
Global Instance: Params (@bi_persistently) 1 := {}.
Global Instance: Params (@bi_later) 1 := {}.

Global Arguments bi_car : simpl never.
Global Arguments bi_dist : simpl never.
Global Arguments bi_equiv : simpl never.
Global Arguments bi_entails {PROP} _ _ : simpl never, rename.
Global Arguments bi_emp {PROP} : simpl never, rename.
Global Arguments bi_pure {PROP} _%_stdpp : simpl never, rename.
Global Arguments bi_and {PROP} _ _ : simpl never, rename.
Global Arguments bi_or {PROP} _ _ : simpl never, rename.
Global Arguments bi_impl {PROP} _ _ : simpl never, rename.
Global Arguments bi_forall {PROP _} _%_I : simpl never, rename.
Global Arguments bi_exist {PROP _} _%_I : simpl never, rename.
Global Arguments bi_sep {PROP} _ _ : simpl never, rename.
Global Arguments bi_wand {PROP} _ _ : simpl never, rename.
Global Arguments bi_persistently {PROP} _ : simpl never, rename.
Global Arguments bi_later {PROP} _ : simpl never, rename.

Global Hint Extern 0 (bi_entails _ _) ⇒ reflexivity : core.

We set this rewrite relation's cost above the stdlib's (impl, iff, eq, ...) and ≡ but below ⊑. eq (at 100) < ≡ (at 150) < bi_entails _ (at 170) < ⊑ (at 200)

Global Instance bi_rewrite_relation (PROP : bi) : RewriteRelation (@bi_entails PROP) | 170 := {}.
Global Instance bi_inhabited {PROP : bi} : Inhabited PROP := populate (bi_pure True).

Notation "'emp'" := (bi_emp) : bi_scope.
Notation "'⌜' φ '⌝'" := (bi_pure φ%type%stdpp) : bi_scope.
Notation "'True'" := (bi_pure True) : bi_scope.
Notation "'False'" := (bi_pure False) : bi_scope.
Infix "∧" := bi_and : bi_scope.
Notation "(∧)" := bi_and (only parsing) : bi_scope.
Infix "∨" := bi_or : bi_scope.
Notation "(∨)" := bi_or (only parsing) : bi_scope.
Infix "→" := bi_impl : bi_scope.
Notation "¬ P" := (P → False)%I : bi_scope.
Infix "∗" := bi_sep : bi_scope.
Notation "(∗)" := bi_sep (only parsing) : bi_scope.
Notation "P -∗ Q" := (bi_wand P Q) : bi_scope.
Notation "∀ x .. y , P" :=
(bi_forall (λ x , .. (bi_forall (λ y , P%I)) ..)) : bi_scope.
Notation "∃ x .. y , P" :=
(bi_exist (λ x , .. (bi_exist (λ y , P%I)) ..)) : bi_scope.
Notation "'<pers>' P" := (bi_persistently P) : bi_scope.

Notation "▷ P" := (bi_later P) : bi_scope.

Notation "P ⊢ Q" := (bi_entails P%I Q%I) : stdpp_scope.
Notation "P '⊢@{' PROP } Q" := (bi_entails (PROP:=PROP) P%I Q%I) (only parsing) : stdpp_scope.
Notation "(⊢)" := bi_entails (only parsing) : stdpp_scope.
Notation "'(⊢@{' PROP } )" := (bi_entails (PROP:=PROP)) (only parsing) : stdpp_scope.

Notation "P ⊣⊢ Q" := (equiv (A:=bi_car _) P%I Q%I) : stdpp_scope.
Notation "P '⊣⊢@{' PROP } Q" := (equiv (A:=bi_car PROP) P%I Q%I) (only parsing) : stdpp_scope.
Notation "(⊣⊢)" := (equiv (A:=bi_car _)) (only parsing) : stdpp_scope.
Notation "'(⊣⊢@{' PROP } )" := (equiv (A:=bi_car PROP)) (only parsing) : stdpp_scope.
Notation "( P ⊣⊢.)" := (equiv (A:=bi_car _) P) (only parsing) : stdpp_scope.
Notation "(.⊣⊢ Q )" := (λ P , P ≡@{bi_car _} Q) (only parsing) : stdpp_scope.

Definition bi_emp_valid {PROP : bi} (P : PROP) : Prop := emp ⊢ P.

Global Arguments bi_emp_valid {_} _%_I : simpl never.
Global Typeclasses Opaque bi_emp_valid.

Notation "⊢ Q" := (bi_emp_valid Q%I) : stdpp_scope.
Notation "'⊢@{' PROP } Q" := (bi_emp_valid (PROP:=PROP) Q%I) (only parsing) : stdpp_scope.

Work around parsing issues: see notation.v for details.