327 lines
9.1 KiB
Coq
327 lines
9.1 KiB
Coq
From Coq Require Import Strings.String.
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From Coq Require Import Lists.List.
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Import ListNotations.
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From Coq Require Import Arith.EqNat.
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Local Open Scope nat_scope.
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Require Import Atom.
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Require Import Metatheory.
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Require Import FSetNotin.
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Require Import terms.
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Inductive type_DeBruijn : Type :=
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| ty_id : string -> type_DeBruijn
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| ty_fvar : atom -> type_DeBruijn
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| ty_bvar : nat -> type_DeBruijn
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| ty_univ : type_DeBruijn -> type_DeBruijn
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| ty_spec : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_func : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_morph : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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| ty_ladder : type_DeBruijn -> type_DeBruijn -> type_DeBruijn
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.
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Inductive expr_DeBruijn : Type :=
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| ex_fvar : atom -> expr_DeBruijn
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| ex_bvar : nat -> expr_DeBruijn
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| ex_ty_abs : expr_DeBruijn -> expr_DeBruijn
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| ex_ty_app : expr_DeBruijn -> type_DeBruijn -> expr_DeBruijn
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| ex_abs : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_morph : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_app : expr_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_let : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_ascend : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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| ex_descend : type_DeBruijn -> expr_DeBruijn -> expr_DeBruijn
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.
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(* get the list of all free variables in a type term *)
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Fixpoint type_fv (τ : type_DeBruijn) {struct τ} : atoms :=
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match τ with
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| ty_id s => {}
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| ty_fvar α => singleton α
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| ty_bvar x => {}
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| ty_univ τ => (type_fv τ)
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| ty_spec σ τ => (type_fv σ) `union` (type_fv τ)
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| ty_func σ τ => (type_fv σ) `union` (type_fv τ)
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| ty_morph σ τ => (type_fv σ) `union` (type_fv τ)
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| ty_ladder σ τ => (type_fv σ) `union` (type_fv τ)
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end.
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(* substitute free variable x with type σ in τ *)
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Fixpoint subst_type (x:atom) (σ:type_DeBruijn) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => if x == s then σ else τ
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| ty_bvar y => ty_bvar y
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| ty_univ τ => ty_univ (subst_type x σ τ)
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| ty_spec τ1 τ2 => ty_spec (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_func τ1 τ2 => ty_func (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_morph τ1 τ2 => ty_morph (subst_type x σ τ1) (subst_type x σ τ2)
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| ty_ladder τ1 τ2 => ty_ladder (subst_type x σ τ1) (subst_type x σ τ2)
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end.
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(* replace a free variable with a new (dangling) bound variable *)
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Fixpoint type_bind_fvar (x:atom) (n:nat) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => if x == s then ty_bvar n else τ
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| ty_bvar n => ty_bvar n
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| ty_univ τ1 => ty_univ (type_bind_fvar x (S n) τ1)
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| ty_spec τ1 τ2 => ty_spec (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_func τ1 τ2 => ty_func (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_morph τ1 τ2 => ty_morph (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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| ty_ladder τ1 τ2 => ty_ladder (type_bind_fvar x n τ1) (type_bind_fvar x n τ2)
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end.
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(* replace (dangling) index with another type *)
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Fixpoint type_open_rec (k:nat) (σ:type_DeBruijn) (τ:type_DeBruijn) {struct τ} : type_DeBruijn :=
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match τ with
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| ty_id s => ty_id s
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| ty_fvar s => ty_fvar s
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| ty_bvar i => if k === i then σ else τ
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| ty_univ τ1 => ty_univ (type_open_rec (S k) σ τ1)
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| ty_spec τ1 τ2 => ty_spec (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_func τ1 τ2 => ty_func (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_morph τ1 τ2 => ty_morph (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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| ty_ladder τ1 τ2 => ty_ladder (type_open_rec k σ τ1) (type_open_rec k σ τ2)
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end.
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Notation "'[' z '~>' u ']' e" := (subst_type z u e) (at level 68).
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Notation "'{' k '~>' σ '}' τ" := (type_open_rec k σ τ) (at level 67).
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Definition type_open σ τ := type_open_rec 0 σ τ.
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(* is the type locally closed ? *)
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Inductive type_lc : type_DeBruijn -> Prop :=
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| Tlc_Id : forall s, type_lc (ty_id s)
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| Tlc_Var : forall s, type_lc (ty_fvar s)
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| Tlc_Univ : forall τ1 L,
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(forall x, (x `notin` L) -> type_lc (type_open (ty_fvar x) τ1)) ->
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type_lc (ty_univ τ1)
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| Tlc_Spec : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_spec τ1 τ2)
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| Tlc_Func : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_func τ1 τ2)
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| Tlc_Morph : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_morph τ1 τ2)
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| Tlc_Ladder : forall τ1 τ2, type_lc τ1 -> type_lc τ2 -> type_lc (ty_ladder τ1 τ2)
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.
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(* number of abstractions *)
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Fixpoint type_debruijn_depth (τ:type_DeBruijn) : nat :=
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match τ with
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| ty_id s => 0
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| ty_fvar s => 0
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| ty_bvar x => 0
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| ty_func s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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| ty_morph s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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| ty_univ t => (1 + (type_debruijn_depth t))
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| ty_spec s t => ((type_debruijn_depth s) - 1)
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| ty_ladder s t => max (type_debruijn_depth s) (type_debruijn_depth t)
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end.
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(*
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Fixpoint type_named2debruijn (τ:type_term) {struct τ} : type_DeBruijn :=
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match τ with
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| type_id s => ty_id s
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| type_var s => ty_fvar (pick fresh )
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| type_univ x t => let t':=(type_named2debruijn t) in (ty_univ (type_bind_fvar x 0 t'))
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| type_spec s t => ty_spec (type_named2debruijn s) (type_named2debruijn t)
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| type_fun s t => ty_func (type_named2debruijn s) (type_named2debruijn t)
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| type_morph s t => ty_morph (type_named2debruijn s) (type_named2debruijn t)
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| type_ladder s t => ty_ladder (type_named2debruijn s) (type_named2debruijn t)
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end.
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Coercion type_named2debruijn : type_term >-> type_DeBruijn.
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*)
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(*
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* Substitution has no effect if the variable is not free
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*)
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Lemma subst_fresh_type : forall (x : atom) (τ:type_DeBruijn) (σ:type_DeBruijn),
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x `notin` (type_fv τ) ->
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([ x ~> σ ] τ) = τ
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.
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Proof.
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intros.
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induction τ.
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- reflexivity.
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- unfold type_fv in H.
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apply AtomSetNotin.elim_notin_singleton in H.
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simpl.
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case_eq (x == a).
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congruence.
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reflexivity.
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- reflexivity.
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- simpl. rewrite IHτ.
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reflexivity.
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apply H.
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- simpl; rewrite IHτ1, IHτ2.
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reflexivity.
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simpl type_fv in H; fsetdec.
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simpl type_fv in H; fsetdec.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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simpl type_fv in H; fsetdec.
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simpl type_fv in H; fsetdec.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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simpl type_fv in H; fsetdec.
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simpl type_fv in H; fsetdec.
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- simpl. rewrite IHτ1, IHτ2.
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reflexivity.
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simpl type_fv in H; fsetdec.
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simpl type_fv in H; fsetdec.
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Qed.
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Lemma open_rec_lc_core : forall τ i σ1 j σ2,
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i <> j ->
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{i ~> σ1} τ = {j ~> σ2} ({i ~> σ1} τ) ->
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({j ~> σ2} τ) = τ.
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Proof with eauto*.
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induction τ;
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intros i σ1 j σ2 Neq H.
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(* id *)
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- reflexivity.
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(* free var *)
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- reflexivity.
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(* bound var *)
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- simpl in *.
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destruct (j === n).
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destruct (i === n).
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3:reflexivity.
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rewrite e,e0 in Neq.
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contradiction Neq.
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reflexivity.
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rewrite H,e.
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simpl.
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destruct (n===n).
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reflexivity.
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contradict n1.
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reflexivity.
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(* univ *)
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- simpl in *.
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inversion H.
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f_equal.
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apply IHτ with (i:=S i) (j:=S j) (σ1:=σ1).
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auto.
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apply H1.
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(* spec *)
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- simpl in *.
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inversion H.
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f_equal.
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* apply IHτ1 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H1.
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* apply IHτ2 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H2.
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(* func *)
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- simpl in *.
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inversion H.
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f_equal.
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* apply IHτ1 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H1.
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* apply IHτ2 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H2.
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(* morph *)
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- simpl in *.
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inversion H.
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f_equal.
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* apply IHτ1 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H1.
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* apply IHτ2 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H2.
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(* ladder *)
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- simpl in *.
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inversion H.
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f_equal.
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* apply IHτ1 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H1.
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* apply IHτ2 with (i:=i) (j:=j) (σ1:=σ1).
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auto.
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apply H2.
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Qed.
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Lemma type_open_rec_lc : forall k σ τ,
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type_lc τ ->
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({ k ~> σ } τ) = τ
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.
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Proof.
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intros.
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generalize dependent k.
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induction H.
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(* id *)
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- auto.
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(* free var *)
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- auto.
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(* univ *)
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- simpl.
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intro k.
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f_equal.
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unfold type_open in *.
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pick fresh x for L.
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apply open_rec_lc_core with
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(i := 0) (σ1 := (ty_fvar x))
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(j := S k) (σ2 := σ).
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trivial.
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apply eq_sym, H0, Fr.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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- simpl. intro. rewrite IHtype_lc1. rewrite IHtype_lc2. reflexivity.
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Qed.
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Lemma type_subst_open_rec : forall τ σ1 σ2 x k,
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type_lc σ2 ->
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[x ~> σ2] ({k ~> σ1} τ)
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=
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{k ~> [x ~> σ2] σ1} ([x ~> σ2] τ).
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Proof.
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induction τ;
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intros; simpl; f_equal; auto.
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(* free var *)
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- destruct (x == a).
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subst.
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apply eq_sym, type_open_rec_lc.
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assumption.
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trivial.
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(* bound var *)
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- destruct (k === n).
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reflexivity.
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trivial.
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Qed.
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