logrel.v 21 KB
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Require Import iris.program_logic.hoare.
Require Import iris.program_logic.lifting.
Require Import iris.algebra.upred_big_op.
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Require Import iris_logrel.F_mu_ref.lang iris_logrel.F_mu_ref.typing
        iris_logrel.F_mu_ref.rules.
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From iris.program_logic Require Export lifting.
From iris.algebra Require Import upred_big_op frac dec_agree.
From iris.program_logic Require Export invariants ghost_ownership.
From iris.program_logic Require Import ownership auth.
Import uPred.

(** interp : is a unary logical relation. *)
Section logrel.
  Context {Σ : gFunctors}.
  Notation "# v" := (of_val v) (at level 20).

  Canonical Structure leibniz_val := leibnizC val.

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  Canonical Structure leibniz_var := leibnizC var.
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  Class Val_to_IProp_Persistent (f : leibniz_val -n> iPropG lang Σ) :=
    val_to_iprop_persistent :  v : val, PersistentP ((cofe_mor_car _ _ f) v).

  Arguments Val_to_IProp_Persistent /.

  (** Just to get nicer closed forms, we define extend_context_interp in three steps. *)
  Program Definition extend_context_interp_fun1
    (τi : leibniz_val -n> iPropG lang Σ)
    (f : leibniz_var -n> leibniz_val -n> iPropG lang Σ) :
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
    {| cofe_mor_car :=
         λ x,
         match x return leibniz_val -n> iPropG lang Σ with
         | O => τi
         | S x' => f x'
         end
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    |}.

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  Program Definition extend_context_interp_fun2
    (τi : leibniz_val -n> iPropG lang Σ) :
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
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    {|
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      cofe_mor_car := λ f, extend_context_interp_fun1 τi f
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    |}.
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  Next Obligation.
  Proof. intros ???? Hfg x; destruct x; cbn; trivial. Qed.
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  Program Definition extend_context_interp :
    (leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
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    {|
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      cofe_mor_car := λ τi, extend_context_interp_fun2 τi
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    |}.
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  Next Obligation.
  Proof. intros n g h H Δ x y. destruct x; cbn; auto. Qed.

  Program Definition extend_context_interp_apply :
    ((leibniz_var -n> leibniz_val -n> iPropG lang Σ)) -n>
    ((leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
     leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ) :=
    {|
      cofe_mor_car := λ Δ,
        {|
          cofe_mor_car := λ f,
            {|
              cofe_mor_car := λ g, f (extend_context_interp g Δ)
            |}
        |}
    |}.
  Solve Obligations with
  repeat intros ?; (cbn + idtac);
    try match goal with [H : _ {_} _|- _] => rewrite H end; trivial.
  Next Obligation.
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  Proof.
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    intros n Δ Δ' HΔ f g x.  cbn.
    match goal with
      |- _ _ ?F x {n} _ _ ?G x =>
      assert (F {n} G) as HFG; [|rewrite HFG; trivial]
    end.
    apply cofe_mor_car_ne; trivial. intros y. cbn.
    destruct y; trivial.
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  Qed.

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  Definition interp_unit : leibniz_val -n> iPropG lang Σ :=
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    {|
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      cofe_mor_car := λ w, (w = UnitV)%I
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    |}.

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  Program Definition interp_prod :
    (leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ) -n>
    leibniz_val -n> iPropG lang Σ :=
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    {|
      cofe_mor_car :=
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        λ τ1i,
        {|
          cofe_mor_car :=
            λ τ2i,
            {|
              cofe_mor_car :=
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                λ w, ( w1 w2, w = PairV w1 w2  τ1i w1  τ2i w2)%I
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            |}
        |}
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    |}.
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  Solve Obligations with
  repeat intros ?; cbn;
    repeat apply exist_ne =>?;
        try match goal with [H : _ {_} _|- _] => rewrite H end; trivial.

  Program Definition interp_sum :
    (leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ) -n>
    leibniz_val -n> iPropG lang Σ :=
    {|
      cofe_mor_car :=
        λ τ1i,
        {|
          cofe_mor_car :=
            λ τ2i,
            {|
              cofe_mor_car :=
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                λ w, (( w1, w = InjLV w1  τ1i w1) 
                      ( w2, w = InjRV w2  τ2i w2))%I
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            |}
        |}
    |}.
  Solve Obligations with
  repeat intros ?; cbn; try apply or_ne;
    try apply exist_ne =>?;
        try match goal with [H : _ {_} _|- _] => rewrite H end; trivial.

  Program Definition interp_arrow :
    (leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ) -n>
    leibniz_val -n> iPropG lang Σ :=
    {|
      cofe_mor_car :=
        λ τ1i,
        {|
          cofe_mor_car :=
            λ τ2i,
            {|
              cofe_mor_car :=
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                λ w, (  v, τ1i v  WP (App (# w) (# v)) @  {{τ2i}})%I
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            |}
        |}
    |}.
  Solve Obligations with
  repeat intros ?; cbn;
    try apply always_ne;
    try apply forall_ne=>?; try apply impl_ne; trivial;
      try apply wp_ne =>?;
          try match goal with [H : _ {_} _|- _] => rewrite H end; trivial.

  Program Definition interp_forall :
    ((leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ)) -n>
    leibniz_val -n> iPropG lang Σ :=
    {|
      cofe_mor_car :=
        λ τi,
        {|
          cofe_mor_car :=
            λ w,
            ( e, w = TLamV e 
                   (τ'i : {f : (leibniz_val -n> iPropG lang Σ) |
                            Val_to_IProp_Persistent f}),
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                     (WP e @  {{λ v, (τi (`τ'i) v)}}))%I
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        |}
    |}.
  Next Obligation.
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  Proof.
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    intros τ τ' x y Hxy; cbn. apply exist_ne => e; apply and_ne; auto.
    rewrite Hxy; trivial.
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  Qed.
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  Next Obligation.
    intros n f g Hfg x; cbn. apply exist_ne => e; apply and_ne; auto.
    apply forall_ne=> P.
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    apply always_ne, wp_ne => w.
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    rewrite Hfg; trivial.
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  Qed.

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  Program Definition interp_rec_pre :
    ((leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ)) -n>
    (leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_val -n> iPropG lang Σ) :=
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    {|
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      cofe_mor_car :=
        λ τi,
        {| cofe_mor_car :=
             λ rec_appr,
             {|
               cofe_mor_car := λ w, ( ( v, w = FoldV v   (τi rec_appr v)))%I
             |}
        |}
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    |}.
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  Next Obligation.
  Proof.
    intros τi rec_appr n x y Hxy; rewrite Hxy; trivial.
  Qed.
  Next Obligation.
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  Proof.
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    intros τi n f g Hfg x. cbn.
    apply always_ne, exist_ne =>w; rewrite Hfg; trivial.
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  Qed.
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  Next Obligation.
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  Proof.
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    intros n τi τi' Hτi f x. cbn.
    apply always_ne, exist_ne =>w; rewrite Hτi; trivial.
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  Qed.
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  Global Instance interp_rec_pre_contr
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         (τi : (leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ))
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    :
      Contractive (interp_rec_pre τi).
  Proof.
    intros n f g H w; cbn.
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    apply always_ne, exist_ne; intros e; apply and_ne; trivial.
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    apply later_contractive =>i Hi.
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    rewrite H; trivial.
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  Qed.

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  Program Definition interp_rec :
    ((leibniz_val -n> iPropG lang Σ) -n> (leibniz_val -n> iPropG lang Σ)) -n>
    (leibniz_val -n> iPropG lang Σ)
    :=
      {|
        cofe_mor_car := λ τi, fixpoint (interp_rec_pre τi)
      |}.
  Next Obligation.
  Proof. intros n f g H; apply fixpoint_ne => z; rewrite H; trivial. Qed.
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  Context `{i : heapG Σ}.
  Context `{L : namespace}.

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  Program Definition interp_ref_pred (l : loc) :
    (leibniz_val -n> iPropG lang Σ) -n> iPropG lang Σ :=
    {|
      cofe_mor_car := λ τi, ( v, l  v  (τi v))%I
    |}.
  Next Obligation.
  Proof. intros ???? H; apply exist_ne =>w; rewrite H; trivial. Qed.
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  Program Definition interp_ref :
    (leibniz_val -n> iPropG lang Σ) -n> leibniz_val -n> iPropG lang Σ :=
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    {|
      cofe_mor_car :=
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        λ τi, {|
          cofe_mor_car :=
            λ w, ( l, w = LocV l  inv (L .@ l) (interp_ref_pred l τi))%I
        |}
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    |}.
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  Next Obligation.
  Proof. intros ???? H; rewrite H; trivial. Qed.
  Next Obligation.
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  Proof.
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    intros ??? H ?; apply exist_ne=>w; apply and_ne; trivial; cbn.
    apply (contractive_ne _); apply exist_ne=>w'; rewrite H; trivial.
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  Qed.

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  Program Fixpoint interp (τ : type) {struct τ}
    : (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n> leibniz_val -n> iPropG lang Σ
    :=
      match τ return (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
                     leibniz_val -n> iPropG lang Σ
      with
      | TUnit => {| cofe_mor_car := λ Δ, interp_unit |}
      | TProd τ1 τ2 => {| cofe_mor_car := λ Δ, interp_prod (interp τ1 Δ) (interp τ2 Δ)|}
      | TSum τ1 τ2 => {| cofe_mor_car := λ Δ, interp_sum(interp τ1 Δ) (interp τ2 Δ)|}
      | TArrow τ1 τ2 => {|cofe_mor_car := λ Δ, interp_arrow (interp τ1 Δ) (interp τ2 Δ)|}
      | TVar v => {| cofe_mor_car :=
                      λ Δ : (leibniz_var -n> (leibniz_val -n> iPropG lang Σ)), (Δ v)  |}
      | TForall τ' =>
        {| cofe_mor_car :=
             λ Δ, interp_forall  (extend_context_interp_apply Δ (interp τ')) |}
      | TRec τ' =>
        {| cofe_mor_car :=
             λ Δ, interp_rec
                    (extend_context_interp_apply Δ (interp τ')) |}
      | Tref τ' => {| cofe_mor_car := λ Δ, interp_ref (interp τ' Δ) |}
      end%I.
  Solve Obligations
  with repeat intros ?; match goal with [H : _ {_} _|- _] => rewrite H end; trivial.

  Class context_interp_Persistent (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
    contextinterppersistent :  v : var, Val_to_IProp_Persistent (Δ v).

  Global Instance Val_to_IProp_Persistent_Persistent
         (f : leibniz_val -n> iPropG lang Σ)
         {Hf : Val_to_IProp_Persistent f}
         (v : val)
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    : PersistentP (f v).
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  Proof. apply Hf. Qed.
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  Global Instance interp_Persistent
         τ (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
         {HΔ : context_interp_Persistent Δ}
    : Val_to_IProp_Persistent (interp τ Δ).
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  Proof.
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    revert Δ HΔ.
    induction τ; cbn; intros Δ HΔ v; try apply _.
    - rewrite /PersistentP /interp_rec fixpoint_unfold /interp_rec_pre; cbn.
      apply always_intro'; trivial.
    - apply Val_to_IProp_Persistent_Persistent; apply HΔ.
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  Qed.

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  Global Instance Persistent_context_interp_rel Δ Γ vs
           {HΔ : context_interp_Persistent Δ}
    : PersistentP (Π∧ zip_with(λ τ v, interp τ Δ v) Γ vs)%I.
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  Proof. typeclasses eauto. Qed.

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  Global Program Instance extend_context_interp_Persistent f Δ
           (Hf : Val_to_IProp_Persistent f)
           {HΔ : context_interp_Persistent Δ}
    : context_interp_Persistent (@extend_context_interp f Δ).
  Next Obligation.
    intros f Δ Hf HΔ v w; destruct v; cbn; trivial.
    apply HΔ.
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  Qed.

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  Local Ltac properness :=
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    repeat
      match goal with
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      | |- ( _: _, _)%I  ( _: _, _)%I => apply exist_proper =>?
      | |- ( _: _, _)%I  ( _: _, _)%I => apply forall_proper =>?
      | |- (_  _)%I  (_  _)%I => apply and_proper
      | |- (_  _)%I  (_  _)%I => apply or_proper
      | |- (_  _)%I  (_  _)%I => apply impl_proper
      | |- (WP _ {{ _ }})%I  (WP _ {{ _ }})%I => apply wp_proper =>?
      | |- ( _)%I  ( _)%I => apply later_proper
      | |- ( _)%I  ( _)%I => apply always_proper
      | |- (inv _ _)%I  (inv _ _)%I => apply (contractive_proper _)
      | |- (_  _)%I  (_  _)%I => apply sep_proper
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      end.

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  Lemma interp_unused_contex_irrel
        (m n : nat)
        (Δ Δ' : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
        (HΔ :  v, Δ (if lt_dec v m then v else (n + v)) 
                     Δ' (if lt_dec v m then v else (n + v)))
        (τ : type)
    :
      interp τ.[iter m up (ren (+n))] Δ  interp τ.[iter m up (ren (+n))] Δ'.
  Proof.
    revert m n Δ Δ' HΔ.
    induction τ; intros m n Δ Δ' HΔ v; cbn; auto.
    - properness; trivial; try apply IHτ1; try apply IHτ2; trivial.
    - properness; trivial; try apply IHτ1; try apply IHτ2; trivial.
    - properness; trivial; try apply IHτ1; try apply IHτ2; trivial.
    - match goal with
        |- _ _ ?f ?x  _ _ ?g ?x =>
        assert (f  g) as Hfg; [|rewrite Hfg; trivial]
      end.
      apply fixpoint_proper => ??; cbn.
      properness; trivial.
      change (up (iter m up (ren (+n)))) with (iter (S m) up (ren (+n))).
      apply IHτ.
      {
        intros x y. destruct x; cbn; trivial.
        destruct lt_dec.
        - specialize (HΔ x); destruct lt_dec; auto with omega.
        - destruct (n + S x) as [|k] eqn:Heq; trivial.
          specialize (HΔ x); destruct lt_dec; auto with omega.
          replace (n + x) with k in HΔ by omega; trivial.
      }
    -  rewrite iter_up. destruct lt_dec; cbn.
       + specialize (HΔ x); destruct lt_dec; auto with omega.
       + asimpl; unfold ids; cbn.
         specialize (HΔ x); destruct lt_dec; auto with omega.
         replace (m + n + (x - m)) with (n + x) by omega. trivial.
    - properness; trivial.
      change (up (iter m up (ren (+n)))) with (iter (S m) up (ren (+n))).
      apply IHτ.
      {
        intros x y. destruct x; cbn; trivial.
        destruct lt_dec.
        - specialize (HΔ x); destruct lt_dec; auto with omega.
        - destruct (n + S x) as [|k] eqn:Heq; trivial.
          specialize (HΔ x); destruct lt_dec; auto with omega.
          replace (n + x) with k in HΔ by omega; trivial.
      }
    - properness; trivial; try apply IHτ; trivial.
  Qed.
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  Program Definition hop_context_interp (m n : nat) :
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
    {| cofe_mor_car :=
         λ Δ,
         {| cofe_mor_car := λ v, if lt_dec v m then Δ v else Δ (v - n) |}
    |}.
  Next Obligation.
  Proof. intros ?????? Hxy; destruct Hxy; trivial. Qed.
  Next Obligation.
  Proof.
    intros ????? Hfg ?; cbn. destruct lt_dec; rewrite Hfg; trivial.
  Qed.
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  Lemma extend_bofore_hop_context_interp (m n : nat)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
        (τi : leibniz_val -n> iPropG lang Σ)
        (v : var)
    :
      (extend_context_interp τi (hop_context_interp m n Δ)
                             (if lt_dec v (S m) then v else n + v))
         (hop_context_interp (S m) n (extend_context_interp τi Δ)
                              (if lt_dec v (S m) then v else n + v)).
  Proof.
    destruct v; cbn; trivial.
    repeat (destruct lt_dec; cbn); auto with omega.
    destruct (n + S v - n) eqn:Heq1;
      destruct (n + S v) eqn:Heq2; try destruct lt_dec; auto with omega.
    match goal with
      [ |- _ _ _ Δ ?a  _ _ _ Δ ?b] => assert (Heq : a = b) by omega; rewrite Heq; trivial
    end.
  Qed.
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  Lemma interp_subst_weaken
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        (m n : nat)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
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        (τ : type)
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    : interp τ Δ  interp τ.[iter m up (ren (+n))] (hop_context_interp m n Δ).
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  Proof.
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    revert m n Δ.
    induction τ; intros m n Δ v; cbn -[extend_context_interp]; auto.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - match goal with
        |- _ _ ?f ?x  _ _ ?g ?x =>
        assert (f  g) as Hfg; [|rewrite Hfg; trivial]
      end.
      apply fixpoint_proper => ??; cbn -[extend_context_interp].
      properness; trivial.
      rewrite IHτ.
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      change (up (iter m up (ren (+n)))) with (iter (S m) up (ren (+n))).
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      apply interp_unused_contex_irrel.
      intros w; rewrite extend_bofore_hop_context_interp; trivial.
    - rewrite iter_up.
      asimpl; unfold ids; cbn; destruct lt_dec; cbn; destruct lt_dec; auto with omega.
      replace (m + n + (x - m)) with (x + n) by omega.
      replace (x + n - n) with x; trivial.
      { (** An incompleteness in omega and lia! *)
        clear.
        replace (x + n) with (n + x) by omega.
        induction n; cbn; auto with omega.
        induction x; cbn; trivial.
      }
    - properness; trivial.
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      change (up (iter m up (ren (+n)))) with (iter (S m) up (ren (+n))).
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      rewrite IHτ.
      apply interp_unused_contex_irrel.
      intros w; rewrite extend_bofore_hop_context_interp; trivial.
    - properness; trivial; try apply IHτ; trivial.
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  Qed.

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  Lemma interp_ren_S (τ : type)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
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        (τi : leibniz_val -n> iPropG lang Σ)
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    : interp τ Δ  interp τ.[ren (+1)] (extend_context_interp τi Δ).
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  Proof.
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    rewrite (interp_subst_weaken 0 1).
    apply interp_unused_contex_irrel.
    { clear. intros [|v]; cbn; trivial. }
  Qed.

  Local Opaque eq_nat_dec.

  Program Definition context_interp_insert (m : nat) :
    (leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) -n>
    (leibniz_var -n> leibniz_val -n> iPropG lang Σ) :=
    {| cofe_mor_car :=
         λ τi,
         {| cofe_mor_car :=
              λ Δ,
              {| cofe_mor_car :=
                   λ v, if lt_dec v m then Δ v else
                          if eq_nat_dec v m then τi else Δ (v - 1)
              |}
         |}
    |}.
  Next Obligation.
  Proof. intros m τi Δ n x y Hxy; destruct Hxy; trivial. Qed.
  Next Obligation.
  Proof.
    intros m τi n Δ Δ' HΔ x; cbn;
      destruct lt_dec; try destruct eq_nat_dec; auto.
  Qed.
  Next Obligation.
  Proof.
    intros m n f g Hfg F Δ x; cbn;
      destruct lt_dec; try destruct eq_nat_dec; auto.
  Qed.

  Lemma extend_context_interp_insert (m : nat)
        (τi : leibniz_val -n> iPropG lang Σ)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
        (Ti : leibniz_val -n> iPropG lang Σ)
    :
      (extend_context_interp Ti (context_interp_insert m τi Δ))
         (context_interp_insert (S m) τi (extend_context_interp Ti Δ)).
  Proof.
    intros [|v]; cbn; trivial.
    repeat destruct lt_dec; trivial;
      repeat destruct eq_nat_dec; cbn; auto with omega.
    destruct v; cbn; auto with omega.
    replace (v - 0) with v by omega; trivial.
  Qed.

  Lemma context_interp_insert_O_extend
        (τi : leibniz_val -n> iPropG lang Σ)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
    :
      (context_interp_insert O τi Δ)
         (extend_context_interp τi Δ).
  Proof.
    intros [|v]; cbn; trivial.
    repeat destruct lt_dec; trivial;
      repeat destruct eq_nat_dec; cbn; auto with omega.
    destruct v; cbn; auto with omega.
  Qed.

  Lemma iter_up_subst_type (m : nat) (τ : type) (x : var) :
      (iter m up (τ .: ids) x) =
      if lt_dec x m then ids x else
        if eq_nat_dec x m then τ.[ren (+m)] else ids (x - 1).
  Proof.
    revert x τ.
    induction m; intros x τ; cbn.
    - destruct x; cbn.
      + destruct eq_nat_dec; auto with omega.
        asimpl; trivial.
      + destruct eq_nat_dec; auto with omega.
    - destruct x; asimpl; trivial.
      rewrite IHm.
      repeat destruct lt_dec; repeat destruct eq_nat_dec;
        asimpl; auto with omega.
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  Qed.

  Lemma interp_subst_iter_up
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        (m : nat)
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
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        (τ : type)
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        (τ' : type)
    : interp τ (context_interp_insert m (interp τ'.[ren (+m)] Δ) Δ)
              interp τ.[iter m up (τ' .: ids)] Δ.
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  Proof.
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    revert m Δ.
    induction τ; intros m Δ v; cbn -[extend_context_interp]; auto.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - properness; trivial; try apply IHτ1; try apply IHτ2.
    - match goal with
        |- _ _ ?f ?x  _ _ ?g ?x =>
        assert (f  g) as Hfg; [|rewrite Hfg; trivial]
      end.
      apply fixpoint_proper => ??; cbn -[extend_context_interp].
      properness; trivial.
      rewrite extend_context_interp_insert.
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      change (up (iter m up (τ' .: ids))) with (iter (S m) up (τ' .: ids)).
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      rewrite -IHτ.
      replace (τ'.[ren (+S m)]) with ((τ'.[ren (+m)]).[ren (+1)]) by (asimpl; trivial).
      rewrite -interp_ren_S; trivial.
    - rewrite iter_up_subst_type.
      repeat destruct lt_dec; repeat destruct eq_nat_dec;
        unfold ids; asimpl; trivial.
    - properness; trivial.
      rewrite extend_context_interp_insert.
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      change (up (iter m up (τ' .: ids))) with (iter (S m) up (τ' .: ids)).
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      rewrite -IHτ.
      replace (τ'.[ren (+S m)]) with ((τ'.[ren (+m)]).[ren (+1)]) by (asimpl; trivial).
      rewrite -interp_ren_S; trivial.
    - properness; trivial; try apply IHτ; trivial.
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  Qed.

  Lemma interp_subst
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        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ)
        (τ : type)
        (τ' : type)
    : interp τ (extend_context_interp (interp τ' Δ) Δ)  interp τ.[τ'/] Δ.
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  Proof.
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    rewrite -(interp_subst_iter_up O Δ τ τ').
    rewrite context_interp_insert_O_extend.
    asimpl; trivial.
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  Qed.

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  Lemma zip_with_context_interp_subst
        (Δ : leibniz_var -n> leibniz_val -n> iPropG lang Σ) (Γ : list type)
        (vs : list leibniz_val) (τi : leibniz_val -n> iPropG lang Σ) :
    ((Π∧ zip_with (λ τ v, interp τ Δ v) Γ vs)%I)
       (Π∧ zip_with (λ τ v, interp τ (extend_context_interp τi Δ) v)
                    (map (λ t : type, t.[ren (+1)]) Γ) vs)%I.
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  Proof.
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    revert Δ vs τi.
    induction Γ as [|Γ]; intros Δ vs τi; cbn; trivial.
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    destruct vs; cbn; trivial.
    apply and_proper.
    - apply interp_ren_S.
    - apply IHΓ.
  Qed.

End logrel.