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From stdpp Require Import gmap base relations.
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From iris Require Import prelude.
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From semantics.ts.stlc_extended Require Import lang notation parallel_subst types bigstep.
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From semantics.ts.stlc_extended Require Import lang notation parallel_subst types bigstep.
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From Equations Require Export Equations.
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(** * Logical relation for the extended STLC *)
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Implicit Types
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(Γ : typing_context)
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(v : val)
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(e : expr)
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(A : type).
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(* *** Definition of the logical relation. *)
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Inductive val_or_expr : Type :=
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| inj_val : val → val_or_expr
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| inj_expr : expr → val_or_expr.
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Equations type_size (A : type) : nat :=
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type_size Int := 1;
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type_size (A → B) := type_size A + type_size B + 1;
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type_size (A × B) := type_size A + type_size B + 1;
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type_size (A + B) := max (type_size A) (type_size B) + 1.
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Equations mut_measure (ve : val_or_expr) (t : type) : nat :=
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mut_measure (inj_val _) t := type_size t;
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mut_measure (inj_expr _) t := 1 + type_size t.
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Equations type_interp (ve : val_or_expr) (t : type) : Prop by wf (mut_measure ve t) := {
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type_interp (inj_val v) Int =>
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∃ z : Z, v = #z ;
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type_interp (inj_val v) (A × B) =>
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(* TODO: add type interpretation *)
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False;
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type_interp (inj_val v) (A + B) =>
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(* TODO: add type interpretation *)
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False;
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type_interp (inj_val v) (A → B) =>
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∃ x e, v = @LamV x e ∧ closed (x :b: nil) e ∧
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∀ v',
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type_interp (inj_val v') A →
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type_interp (inj_expr (subst' x v' e)) B;
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type_interp (inj_expr e) t =>
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∃ v, big_step e v ∧ type_interp (inj_val v) t
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}.
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Next Obligation.
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repeat simp mut_measure; simp type_size; lia.
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Qed.
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Next Obligation.
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simp mut_measure. simp type_size.
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destruct A; repeat simp mut_measure; repeat simp type_size; lia.
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Qed.
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(* Uncomment the following once you have amended the type interpretation to
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solve the new obligations: *)
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(*
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Next Obligation. repeat simp mut_measure; simp type_size; lia. Qed.
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Next Obligation. repeat simp mut_measure; simp type_size; lia. Qed.
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Next Obligation. repeat simp mut_measure; simp type_size; lia. Qed.
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Next Obligation. repeat simp mut_measure; simp type_size; lia. Qed.
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*)
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Notation sem_val_rel t v := (type_interp (inj_val v) t).
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Notation sem_expr_rel t e := (type_interp (inj_expr e) t).
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Notation 𝒱 t v := (sem_val_rel t v).
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Notation ℰ t v := (sem_expr_rel t v).
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(* *** Semantic typing of contexts *)
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Implicit Types
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(θ : gmap string expr).
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Inductive sem_context_rel : typing_context → (gmap string expr) → Prop :=
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| sem_context_rel_empty : sem_context_rel ∅ ∅
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| sem_context_rel_insert Γ θ v x A :
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𝒱 A v →
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sem_context_rel Γ θ →
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sem_context_rel (<[x := A]> Γ) (<[x := of_val v]> θ).
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Notation 𝒢 := sem_context_rel.
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Definition sem_typed Γ e A :=
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closed (elements (dom Γ)) e ∧
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∀ θ, 𝒢 Γ θ → ℰ A (subst_map θ e).
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Notation "Γ ⊨ e : A" := (sem_typed Γ e A) (at level 74, e, A at next level).
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(* We start by proving a couple of helper lemmas that will be useful later. *)
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Lemma sem_expr_rel_of_val A v:
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ℰ A v → 𝒱 A v.
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Proof.
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simp type_interp.
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intros (v' & ->%big_step_val & Hv').
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apply Hv'.
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Qed.
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Lemma val_inclusion A v:
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𝒱 A v → ℰ A v.
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Proof.
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intros H. simp type_interp. eauto using big_step_of_val.
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Qed.
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Lemma val_rel_closed v A:
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𝒱 A v → closed [] v.
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Proof.
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induction A in v |-*; simp type_interp.
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- intros [z ->]. done.
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- intros (x & e & -> & Hcl & _). done.
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(* TODO: exercise *)
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Admitted.
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Lemma sem_context_rel_closed Γ θ:
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𝒢 Γ θ → subst_closed [] θ.
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Proof.
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induction 1; rewrite /subst_closed.
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- naive_solver.
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- intros y e. rewrite lookup_insert_Some.
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intros [[-> <-]|[Hne Hlook]].
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+ by eapply val_rel_closed.
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+ eapply IHsem_context_rel; last done.
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Qed.
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(* This is essentially an inversion lemma for 𝒢 *)
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Lemma sem_context_rel_vals Γ θ x A :
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𝒢 Γ θ →
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Γ !! x = Some A →
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∃ e v, θ !! x = Some e ∧ to_val e = Some v ∧ 𝒱 A v.
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Proof.
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induction 1 as [|Γ θ v y B Hvals Hctx IH].
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- naive_solver.
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- rewrite lookup_insert_Some. intros [[-> ->]|[Hne Hlook]].
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+ do 2 eexists. split; first by rewrite lookup_insert.
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split; first by eapply to_of_val. done.
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+ eapply IH in Hlook as (e & w & Hlook & He & Hval).
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do 2 eexists; split; first by rewrite lookup_insert_ne.
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split; first done. done.
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Qed.
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Lemma sem_context_rel_dom Γ θ :
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𝒢 Γ θ → dom Γ = dom θ.
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Proof.
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induction 1.
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- by rewrite !dom_empty.
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- rewrite !dom_insert. congruence.
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Qed.
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(* *** Compatibility lemmas *)
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Lemma compat_int Γ z : Γ ⊨ (LitInt z) : Int.
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Proof.
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split; first done.
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intros θ _. simp type_interp.
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exists #z. split; simpl.
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- constructor.
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- simp type_interp. eauto.
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Qed.
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Lemma compat_var Γ x A :
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Γ !! x = Some A →
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Γ ⊨ (Var x) : A.
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Proof.
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intros Hx. split.
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{ eapply bool_decide_pack, elem_of_elements, elem_of_dom_2, Hx. }
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intros θ Hctx; simpl.
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eapply sem_context_rel_vals in Hx as (e & v & He & Heq & Hv); last done.
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rewrite He. simp type_interp. exists v. split; last done.
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rewrite -(of_to_val _ _ Heq).
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by apply big_step_of_val.
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Qed.
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Lemma compat_app Γ e1 e2 A B :
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Γ ⊨ e1 : (A → B) →
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Γ ⊨ e2 : A →
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Γ ⊨ (e1 e2) : B.
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Proof.
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intros [Hfuncl Hfun] [Hargcl Harg]. split.
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{ unfold closed. simpl. eauto. }
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intros θ Hctx; simpl.
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specialize (Hfun _ Hctx). simp type_interp in Hfun. destruct Hfun as (v1 & Hbs1 & Hv1).
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simp type_interp in Hv1. destruct Hv1 as (x & e & -> & Hcl & Hv1).
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specialize (Harg _ Hctx). simp type_interp in Harg.
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destruct Harg as (v2 & Hbs2 & Hv2).
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apply Hv1 in Hv2.
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simp type_interp in Hv2. destruct Hv2 as (v & Hbsv & Hv).
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simp type_interp.
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exists v. split; last done.
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eauto.
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Qed.
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(* Compatibility for [lam] unfortunately needs a very technical helper lemma. *)
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Lemma lam_closed Γ θ (x : string) A e :
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closed (elements (dom (<[x:=A]> Γ))) e →
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𝒢 Γ θ →
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closed [] (Lam x (subst_map (delete x θ) e)).
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Proof.
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intros Hcl Hctxt.
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eapply subst_map_closed'_2.
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- eapply is_closed_weaken; first done.
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rewrite dom_delete dom_insert (sem_context_rel_dom Γ θ) //.
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intros y. destruct (decide (x = y)); set_solver.
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- eapply subst_closed_weaken, sem_context_rel_closed; last done.
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+ set_solver.
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+ apply map_delete_subseteq.
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Qed.
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Lemma compat_lam Γ x e A B :
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(<[ x := A ]> Γ) ⊨ e : B →
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Γ ⊨ (Lam (BNamed x) e) : (A → B).
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Proof.
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intros [Hbodycl Hbody]. split.
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{ unfold closed in *. cbn in *. eapply is_closed_weaken; first eassumption.
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set_solver. }
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intros θ Hctxt. simpl. simp type_interp.
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eexists.
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split; first by eauto.
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simp type_interp.
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eexists x, _. split; first reflexivity.
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split; first by eapply lam_closed.
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intros v' Hv'.
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specialize (Hbody (<[ x := of_val v']> θ)).
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simpl. rewrite subst_subst_map; last by eapply sem_context_rel_closed.
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apply Hbody.
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apply sem_context_rel_insert; done.
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Qed.
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Lemma compat_lam_anon Γ e A B :
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Γ ⊨ e : B →
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Γ ⊨ (Lam BAnon e) : (A → B).
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Proof.
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intros [Hbodycl Hbody]. split; first done.
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intros θ Hctxt. simpl. simp type_interp.
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eexists.
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split; first by eauto.
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simp type_interp.
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eexists _, _. split; first reflexivity.
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split.
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{ simpl. eapply subst_map_closed'_2; simpl.
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- by erewrite <-sem_context_rel_dom.
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- by eapply sem_context_rel_closed. }
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naive_solver.
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Qed.
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Lemma compat_add Γ e1 e2 :
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Γ ⊨ e1 : Int →
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Γ ⊨ e2 : Int →
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Γ ⊨ (e1 + e2) : Int.
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Proof.
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intros [Hcl1 He1] [Hcl2 He2]. split.
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{ unfold closed in *. naive_solver. }
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intros θ Hctx.
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simp type_interp.
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specialize (He1 _ Hctx). specialize (He2 _ Hctx).
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simp type_interp in He1. simp type_interp in He2.
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destruct He1 as (v1 & Hb1 & Hv1).
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destruct He2 as (v2 & Hb2 & Hv2).
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simp type_interp in Hv1, Hv2.
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destruct Hv1 as (z1 & ->). destruct Hv2 as (z2 & ->).
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exists #(z1 + z2). split.
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- constructor; done.
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- exists (z1 + z2)%Z. done.
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Qed.
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Lemma sem_soundness Γ e A :
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(Γ ⊢ e : A)%ty →
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Γ ⊨ e : A.
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Proof.
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induction 1.
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- by apply compat_var.
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- by apply compat_lam.
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- by apply compat_lam_anon.
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- apply compat_int.
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- by eapply compat_app.
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- by apply compat_add.
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(* add compatibility lemmas for the new rules here. *)
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(* TODO: exercise *)
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Admitted.
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Lemma termination e A :
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(∅ ⊢ e : A)%ty →
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∃ v, big_step e v.
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Proof.
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intros [Hsemcl Hsem]%sem_soundness.
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specialize (Hsem ∅).
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simp type_interp in Hsem.
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rewrite subst_map_empty in Hsem.
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destruct Hsem as (v & Hbs & _); last eauto.
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constructor.
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Qed.
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