From 00a0ce9082b4cc1389815defcc806efd4a9b80f4 Mon Sep 17 00:00:00 2001
From: Greg Brown <greg.brown@cl.cam.ac.uk>
Date: Mon, 18 Apr 2022 15:05:24 +0100
Subject: Do a big refactor.

- Replace the decidable predicates on expressions and statements with
  separate data types.

- Reorganise the Hoare logic semantics to remove unnecessary
  definitions.

- Make liberal use of modules to group related definitions together.

- Unify the types for denotational and Hoare logic semantics.

- Make bits an abstraction of array types.
---
 src/Helium/Semantics/Axiomatic/Term.agda | 873 ++++++++++++++++++-------------
 1 file changed, 515 insertions(+), 358 deletions(-)

(limited to 'src/Helium/Semantics/Axiomatic/Term.agda')

diff --git a/src/Helium/Semantics/Axiomatic/Term.agda b/src/Helium/Semantics/Axiomatic/Term.agda
index c9ddd02..08eac5f 100644
--- a/src/Helium/Semantics/Axiomatic/Term.agda
+++ b/src/Helium/Semantics/Axiomatic/Term.agda
@@ -13,373 +13,530 @@ module Helium.Semantics.Axiomatic.Term
   (rawPseudocode : RawPseudocode b₁ b₂ i₁ i₂ i₃ r₁ r₂ r₃)
   where
 
+
 open RawPseudocode rawPseudocode
 
 import Data.Bool as Bool
-open import Data.Fin as Fin using (Fin; suc)
-import Data.Fin.Properties as Finₚ
+open import Data.Empty using (⊥-elim)
+open import Data.Fin as Fin using (Fin; suc; punchOut)
 open import Data.Fin.Patterns
-open import Data.Nat as ℕ using (ℕ; suc)
+import Data.Integer as 𝕀
+import Data.Fin.Properties as Finₚ
+open import Data.Nat as ℕ using (ℕ; suc; _≤_; z≤n; s≤s; _⊔_)
 import Data.Nat.Properties as ℕₚ
-open import Data.Product using (∃; _×_; _,_; proj₁; proj₂; uncurry; dmap)
-open import Data.Vec as Vec using (Vec; []; _∷_; _++_; lookup)
-import Data.Vec.Functional as VecF
+open import Data.Product using (∃; _,_; dmap)
+open import Data.Vec as Vec using (Vec; []; _∷_; _++_; lookup; insert; remove; map; zipWith; take; drop)
 import Data.Vec.Properties as Vecₚ
+open import Data.Vec.Recursive as Vecᵣ using (2+_)
 open import Data.Vec.Relation.Unary.All as All using (All; []; _∷_)
-open import Function using (_∘_; _∘₂_; id; flip)
+open import Function
 open import Helium.Data.Pseudocode.Core
-import Helium.Data.Pseudocode.Manipulate as M
-open import Helium.Semantics.Axiomatic.Core rawPseudocode
-open import Level using (_⊔_; lift; lower)
-open import Relation.Binary.PropositionalEquality hiding ([_]) renaming (subst to ≡-subst)
-open import Relation.Nullary using (¬_; does; yes; no)
-open import Relation.Nullary.Decidable.Core using (True; toWitness)
-open import Relation.Nullary.Negation using (contradiction)
+open import Helium.Data.Pseudocode.Manipulate hiding (module Cast)
+open import Helium.Semantics.Core rawPseudocode
+open import Level as L using (lift; lower)
+open import Relation.Binary.PropositionalEquality hiding (subst)
+open import Relation.Nullary using (does; yes; no)
 
 private
   variable
-    t t′ t₁ t₂ : Type
-    m n o      : ℕ
-    Γ Δ Σ ts   : Vec Type m
-
-data Term (Σ : Vec Type o) (Γ : Vec Type n) (Δ : Vec Type m) : Type → Set (b₁ ⊔ i₁ ⊔ r₁) where
-  state : ∀ i → Term Σ Γ Δ (lookup Σ i)
-  var   : ∀ i → Term Σ Γ Δ (lookup Γ i)
-  meta  : ∀ i → Term Σ Γ Δ (lookup Δ i)
-  func  : Transform ts t → All (Term Σ Γ Δ) ts → Term Σ Γ Δ t
-
-castType : Term Σ Γ Δ t → t ≡ t′ → Term Σ Γ Δ t′
-castType (state i)   refl = state i
-castType (var i)     refl = var i
-castType (meta i)    refl = meta i
-castType (func f ts) eq   = func (≡-subst (Transform _) eq f) ts
-
-substState : Term Σ Γ Δ t → ∀ i → Term Σ Γ Δ (lookup Σ i) → Term Σ Γ Δ t
-substState (state i) j t′ with i Fin.≟ j
-... | yes refl = t′
-... | no _     = state i
-substState (var i) j t′ = var i
-substState (meta i) j t′ = meta i
-substState (func f ts) j t′ = func f (helper ts j t′)
-  where
-  helper : ∀ {n ts} → All (Term Σ Γ Δ) {n} ts → ∀ i → Term Σ Γ Δ (lookup Σ i) → All (Term Σ Γ Δ) ts
-  helper []       i t′ = []
-  helper (t ∷ ts) i t′ = substState t i t′ ∷ helper ts i t′
-
-substVar : Term Σ Γ Δ t → ∀ i → Term Σ Γ Δ (lookup Γ i) → Term Σ Γ Δ t
-substVar (state i) j t′ = state i
-substVar (var i) j t′ with i Fin.≟ j
-... | yes refl = t′
-... | no _     = var i
-substVar (meta i) j t′ = meta i
-substVar (func f ts) j t′ = func f (helper ts j t′)
-  where
-  helper : ∀ {n ts} → All (Term Σ Γ Δ) {n} ts → ∀ i → Term Σ Γ Δ (lookup Γ i) → All (Term Σ Γ Δ) ts
-  helper []       i t′ = []
-  helper (t ∷ ts) i t′ = substVar t i t′ ∷ helper ts i t′
-
-substVars : Term Σ Γ Δ t → All (Term Σ ts Δ) Γ → Term Σ ts Δ t
-substVars (state i)    ts = state i
-substVars (var i)      ts = All.lookup i ts
-substVars (meta i)     ts = meta i
-substVars (func f ts′) ts = func f (helper ts′ ts)
-  where
-  helper : ∀ {ts ts′} → All (Term Σ Γ Δ) {n} ts → All (Term {n = m} Σ ts′ Δ) Γ → All (Term Σ ts′ Δ) ts
-  helper []        ts = []
-  helper (t ∷ ts′) ts = substVars t ts ∷ helper ts′ ts
-
-elimVar : Term Σ (t′ ∷ Γ) Δ t → Term Σ Γ Δ t′ → Term Σ Γ Δ t
-elimVar (state i)     t′ = state i
-elimVar (var 0F)      t′ = t′
-elimVar (var (suc i)) t′ = var i
-elimVar (meta i)      t′ = meta i
-elimVar (func f ts)   t′ = func f (helper ts t′)
-  where
-  helper : ∀ {n ts} → All (Term Σ (_ ∷ Γ) Δ) {n} ts → Term Σ Γ Δ _ → All (Term Σ Γ Δ) ts
-  helper []       t′ = []
-  helper (t ∷ ts) t′ = elimVar t t′ ∷ helper ts t′
-
-wknVar : Term Σ Γ Δ t → Term Σ (t′ ∷ Γ) Δ t
-wknVar (state i)   = state i
-wknVar (var i)     = var (suc i)
-wknVar (meta i)    = meta i
-wknVar (func f ts) = func f (helper ts)
-  where
-  helper : ∀ {n ts} → All (Term Σ Γ Δ) {n} ts → All (Term Σ (_ ∷ Γ) Δ) ts
-  helper []       = []
-  helper (t ∷ ts) = wknVar t ∷ helper ts
-
-wknVars : (ts : Vec Type n) → Term Σ Γ Δ t → Term Σ (ts ++ Γ) Δ t
-wknVars τs (state i)   = state i
-wknVars τs (var i)     = castType (var (Fin.raise (Vec.length τs) i)) (Vecₚ.lookup-++ʳ τs _ i)
-wknVars τs (meta i)    = meta i
-wknVars τs (func f ts) = func f (helper ts)
-  where
-  helper : ∀ {n ts} → All (Term Σ Γ Δ) {n} ts → All (Term Σ (τs ++ Γ) Δ) ts
-  helper []       = []
-  helper (t ∷ ts) = wknVars τs t ∷ helper ts
-
-addVars : Term Σ [] Δ t → Term Σ Γ Δ t
-addVars (state i)   = state i
-addVars (meta i)    = meta i
-addVars (func f ts) = func f (helper ts)
-  where
-  helper : ∀ {n ts} → All (Term Σ [] Δ) {n} ts → All (Term Σ Γ Δ) ts
-  helper []       = []
-  helper (t ∷ ts) = addVars t ∷ helper ts
-
-wknMetaAt : ∀ i → Term Σ Γ Δ t → Term Σ Γ (Vec.insert Δ i t′) t
-wknMetaAt′ : ∀ i → All (Term Σ Γ Δ) ts → All (Term Σ Γ (Vec.insert Δ i t′)) ts
-
-wknMetaAt i (state j)   = state j
-wknMetaAt i (var j)     = var j
-wknMetaAt i (meta j)    = castType (meta (Fin.punchIn i j)) (Vecₚ.insert-punchIn _ i _ j)
-wknMetaAt i (func f ts) = func f (wknMetaAt′ i ts)
-
-wknMetaAt′ i []       = []
-wknMetaAt′ i (t ∷ ts) = wknMetaAt i t ∷ wknMetaAt′ i ts
-
-wknMeta : Term Σ Γ Δ t → Term Σ Γ (t′ ∷ Δ) t
-wknMeta = wknMetaAt 0F
-
-wknMeta′ : All (Term Σ Γ Δ) ts → All (Term Σ Γ (t′ ∷ Δ)) ts
-wknMeta′ = wknMetaAt′ 0F
-
-wknMetas : (ts : Vec Type n) → Term Σ Γ Δ t → Term Σ Γ (ts ++ Δ) t
-wknMetas τs (state i)   = state i
-wknMetas τs (var i)     = var i
-wknMetas τs (meta i)    = castType (meta (Fin.raise (Vec.length τs) i)) (Vecₚ.lookup-++ʳ τs _ i)
-wknMetas τs (func f ts) = func f (helper ts)
-  where
-  helper : ∀ {n ts} → All (Term Σ Γ Δ) {n} ts → All (Term Σ Γ (τs ++ Δ)) ts
-  helper []       = []
-  helper (t ∷ ts) = wknMetas τs t ∷ helper ts
-
-func₀ : ⟦ t ⟧ₜ → Term Σ Γ Δ t
-func₀ f = func (λ _ → f) []
-
-func₁ : (⟦ t ⟧ₜ → ⟦ t′ ⟧ₜ) → Term Σ Γ Δ t → Term Σ Γ Δ t′
-func₁ f t = func (λ (x , _) → f x) (t ∷ [])
-
-func₂ : (⟦ t₁ ⟧ₜ → ⟦ t₂ ⟧ₜ → ⟦ t′ ⟧ₜ) → Term Σ Γ Δ t₁ → Term Σ Γ Δ t₂ → Term Σ Γ Δ t′
-func₂ f t₁ t₂ = func (λ (x , y , _) → f x y) (t₁ ∷ t₂ ∷ [])
-
-[_][_≟_] : HasEquality t → Term Σ Γ Δ t → Term Σ Γ Δ t → Term Σ Γ Δ bool
-[ bool ][ t ≟ t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x Bool.≟ y))) t t′
-[ int ][ t ≟ t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x ≟ᶻ y))) t t′
-[ fin ][ t ≟ t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x Fin.≟ y))) t t′
-[ real ][ t ≟ t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x ≟ʳ y))) t t′
-[ bit ][ t ≟ t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x ≟ᵇ₁ y))) t t′
-[ bits ][ t ≟ t′ ] = func₂ (λ xs ys → lift (does (VecF.fromVec (Vec.map lower xs) ≟ᵇ VecF.fromVec (Vec.map lower ys)))) t t′
-
-[_][_<?_] : IsNumeric t → Term Σ Γ Δ t → Term Σ Γ Δ t → Term Σ Γ Δ bool
-[ int ][ t <? t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x <ᶻ? y))) t t′
-[ real ][ t <? t′ ] = func₂ (λ (lift x) (lift y) → lift (does (x <ʳ? y))) t t′
-
-[_][_] : ∀ t → Term Σ Γ Δ (elemType t) → Term Σ Γ Δ (asType t 1)
-[ bits ][ t ] = func₁ (_∷ []) t
-[ array τ ][ t ] = func₁ (_∷ []) t
-
-unbox : ∀ t → Term Σ Γ Δ (asType t 1) → Term Σ Γ Δ (elemType t)
-unbox bits = func₁ Vec.head
-unbox (array t) = func₁ Vec.head
-
-castV : ∀ {a} {A : Set a} {m n} → .(eq : m ≡ n) → Vec A m → Vec A n
-castV {n = 0}     eq []       = []
-castV {n = suc n} eq (x ∷ xs) = x ∷ castV (ℕₚ.suc-injective eq) xs
-
-cast′ : ∀ t → .(eq : m ≡ n) → ⟦ asType t m ⟧ₜ → ⟦ asType t n ⟧ₜ
-cast′ bits      eq = castV eq
-cast′ (array τ) eq = castV eq
-
-cast : ∀ t → .(eq : m ≡ n) → Term Σ Γ Δ (asType t m) → Term Σ Γ Δ (asType t n)
-cast τ eq = func₁ (cast′ τ eq)
-
-[_][-_] : IsNumeric t → Term Σ Γ Δ t → Term Σ Γ Δ t
-[ int ][- t ] = func₁ (lift ∘ ℤ.-_ ∘ lower) t
-[ real ][- t ] = func₁ (lift ∘ ℝ.-_ ∘ lower) t
-
-[_,_,_,_][_+_] : ∀ t₁ t₂ → (isNum₁ : True (isNumeric? t₁)) → (isNum₂ : True (isNumeric? t₂)) → Term Σ Γ Δ t₁ → Term Σ Γ Δ t₂ → Term Σ Γ Δ (combineNumeric t₁ t₂ isNum₁ isNum₂)
-[ int , int , _ , _ ][ t + t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℤ.+ y)) t t′
-[ int , real , _ , _ ][ t + t′ ] = func₂ (λ (lift x) (lift y) → lift (x /1 ℝ.+ y)) t t′
-[ real , int , _ , _ ][ t + t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℝ.+ y /1)) t t′
-[ real , real , _ , _ ][ t + t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℝ.+ y)) t t′
-
-[_,_,_,_][_*_] : ∀ t₁ t₂ → (isNum₁ : True (isNumeric? t₁)) → (isNum₂ : True (isNumeric? t₂)) → Term Σ Γ Δ t₁ → Term Σ Γ Δ t₂ → Term Σ Γ Δ (combineNumeric t₁ t₂ isNum₁ isNum₂)
-[ int , int , _ , _ ][ t * t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℤ.* y)) t t′
-[ int , real , _ , _ ][ t * t′ ] = func₂ (λ (lift x) (lift y) → lift (x /1 ℝ.* y)) t t′
-[ real , int , _ , _ ][ t * t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℝ.* y /1)) t t′
-[ real , real , _ , _ ][ t * t′ ] = func₂ (λ (lift x) (lift y) → lift (x ℝ.* y)) t t′
-
-[_][_^_] : IsNumeric t → Term Σ Γ Δ t → ℕ → Term Σ Γ Δ t
-[ int ][ t ^ n ] = func₁ (lift ∘ (ℤ′._^′ n) ∘ lower) t
-[ real ][ t ^ n ] = func₁ (lift ∘ (ℝ′._^′ n) ∘ lower) t
-
-2≉0 : Set _
-2≉0 = ¬ 2 ℝ′.×′ 1ℝ ℝ.≈ 0ℝ
-
-[_][_>>_] : 2≉0 → Term Σ Γ Δ int → ℕ → Term Σ Γ Δ int
-[ 2≉0 ][ t >> n ] = func₁ (lift ∘ ⌊_⌋ ∘ (ℝ._* 2≉0 ℝ.⁻¹ ℝ′.^′ n) ∘ _/1 ∘ lower) t
-
--- 0 of y is 0 of result
-join′ : ∀ t → ⟦ asType t m ⟧ₜ → ⟦ asType t n ⟧ₜ → ⟦ asType t (n ℕ.+ m) ⟧ₜ
-join′ bits      = flip _++_
-join′ (array t) = flip _++_
-
-take′ : ∀ t m {n} → ⟦ asType t (m ℕ.+ n) ⟧ₜ → ⟦ asType t m ⟧ₜ
-take′ bits      m = Vec.take m
-take′ (array t) m = Vec.take m
-
-drop′ : ∀ t m {n} → ⟦ asType t (m ℕ.+ n) ⟧ₜ → ⟦ asType t n ⟧ₜ
-drop′ bits      m = Vec.drop m
-drop′ (array t) m = Vec.drop m
-
-private
-  m≤n⇒m+k≡n : ∀ {m n} → m ℕ.≤ n → ∃ λ k → m ℕ.+ k ≡ n
-  m≤n⇒m+k≡n ℕ.z≤n       = _ , refl
-  m≤n⇒m+k≡n (ℕ.s≤s m≤n) = dmap id (cong suc) (m≤n⇒m+k≡n m≤n)
-
-  slicedSize : ∀ n m (i : Fin (suc n)) → ∃ λ k → n ℕ.+ m ≡ Fin.toℕ i ℕ.+ (m ℕ.+ k) × Fin.toℕ i ℕ.+ k ≡ n
-  slicedSize n m i = k , (begin
-    n ℕ.+ m                 ≡˘⟨ cong (ℕ._+ m) (proj₂ i+k≡n) ⟩
-    (Fin.toℕ i ℕ.+ k) ℕ.+ m ≡⟨  ℕₚ.+-assoc (Fin.toℕ i) k m ⟩
-    Fin.toℕ i ℕ.+ (k ℕ.+ m) ≡⟨  cong (Fin.toℕ i ℕ.+_) (ℕₚ.+-comm k m) ⟩
-    Fin.toℕ i ℕ.+ (m ℕ.+ k) ∎) ,
-    proj₂ i+k≡n
-    where
-    open ≡-Reasoning
-    i+k≡n = m≤n⇒m+k≡n (ℕₚ.≤-pred (Finₚ.toℕ<n i))
-    k = proj₁ i+k≡n
-
--- 0 of x is i of result
-splice′ : ∀ t → ⟦ asType t m ⟧ₜ → ⟦ asType t n ⟧ₜ → ⟦ fin (suc n) ⟧ₜ → ⟦ asType t (n ℕ.+ m) ⟧ₜ
-splice′ {m = m} t x y (lift i) = cast′ t eq (join′ t (join′ t high x) low)
+    t t′ t₁ t₂  : Type
+    i j k m n o : ℕ
+    Γ Δ Σ ts    : Vec Type m
+
+  ℓ = b₁ L.⊔ i₁ L.⊔ r₁
+
+  punchOut-insert : ∀ {a} {A : Set a} (xs : Vec A n) {i j} (i≢j : i ≢ j) x → lookup xs (punchOut i≢j) ≡ lookup (insert xs i x) j
+  punchOut-insert xs {i} {j} i≢j x = begin
+    lookup xs (punchOut i≢j)                         ≡˘⟨ cong (flip lookup (punchOut i≢j)) (Vecₚ.remove-insert xs i x) ⟩
+    lookup (remove (insert xs i x) i) (punchOut i≢j) ≡⟨  Vecₚ.remove-punchOut (insert xs i x) i≢j ⟩
+    lookup (insert xs i x) j                         ∎
+    where open ≡-Reasoning
+
+  open ℕₚ.≤-Reasoning
+
+  ⨆[_]_ : ∀ n → ℕ Vecᵣ.^ n → ℕ
+  ⨆[_]_ = Vecᵣ.foldl (const ℕ) 0 id (const (flip ℕ._⊔_))
+
+  ⨆-step : ∀ m x xs → ⨆[ 2+ m ] (x , xs) ≡ x ⊔ ⨆[ suc m ] xs
+  ⨆-step 0       x xs       = refl
+  ⨆-step (suc m) x (y , xs) = begin-equality
+    ⨆[ 2+ suc m ] (x , y , xs) ≡⟨  ⨆-step m (x ⊔ y) xs ⟩
+    x ⊔ y ⊔ ⨆[ suc m ] xs      ≡⟨  ℕₚ.⊔-assoc x y _ ⟩
+    x ⊔ (y ⊔ ⨆[ suc m ] xs)    ≡˘⟨ cong (_ ⊔_) (⨆-step m y xs) ⟩
+    x ⊔ ⨆[ 2+ m ] (y , xs)     ∎
+
+  lookup-⨆-≤ : ∀ i (xs : ℕ Vecᵣ.^ n) → Vecᵣ.lookup i xs ≤ ⨆[ n ] xs
+  lookup-⨆-≤ {1}    0F      x        = ℕₚ.≤-refl
+  lookup-⨆-≤ {2+ n} 0F      (x , xs) = begin
+    x                  ≤⟨  ℕₚ.m≤m⊔n x _ ⟩
+    x ⊔ ⨆[ suc n ] xs  ≡˘⟨ ⨆-step n x xs ⟩
+    ⨆[ 2+ n ] (x , xs) ∎
+  lookup-⨆-≤ {2+ n} (suc i) (x , xs) = begin
+    Vecᵣ.lookup i xs   ≤⟨  lookup-⨆-≤ i xs ⟩
+    ⨆[ suc n ] xs      ≤⟨  ℕₚ.m≤n⊔m x _ ⟩
+    x ⊔ ⨆[ suc n ] xs  ≡˘⟨ ⨆-step n x xs ⟩
+    ⨆[ 2+ n ] (x , xs) ∎
+
+data Term (Σ : Vec Type i) (Γ : Vec Type j) (Δ : Vec Type k) : Type → Set ℓ where
+  lit           : ⟦ t ⟧ₜ → Term Σ Γ Δ t
+  state         : ∀ i → Term Σ Γ Δ (lookup Σ i)
+  var           : ∀ i → Term Σ Γ Δ (lookup Γ i)
+  meta          : ∀ i → Term Σ Γ Δ (lookup Δ i)
+  _≟_           : ⦃ HasEquality t ⦄ → Term Σ Γ Δ t → Term Σ Γ Δ t → Term Σ Γ Δ bool
+  _<?_          : ⦃ Ordered t ⦄ → Term Σ Γ Δ t → Term Σ Γ Δ t → Term Σ Γ Δ bool
+  inv           : Term Σ Γ Δ bool → Term Σ Γ Δ bool
+  _&&_          : Term Σ Γ Δ bool → Term Σ Γ Δ bool → Term Σ Γ Δ bool
+  _||_          : Term Σ Γ Δ bool → Term Σ Γ Δ bool → Term Σ Γ Δ bool
+  not           : Term Σ Γ Δ (bits n) → Term Σ Γ Δ (bits n)
+  _and_         : Term Σ Γ Δ (bits n) → Term Σ Γ Δ (bits n) → Term Σ Γ Δ (bits n)
+  _or_          : Term Σ Γ Δ (bits n) → Term Σ Γ Δ (bits n) → Term Σ Γ Δ (bits n)
+  [_]           : Term Σ Γ Δ t → Term Σ Γ Δ (array t 1)
+  unbox         : Term Σ Γ Δ (array t 1) → Term Σ Γ Δ t
+  merge         : Term Σ Γ Δ (array t m) → Term Σ Γ Δ (array t n) → Term Σ Γ Δ (fin (suc n)) → Term Σ Γ Δ (array t (n ℕ.+ m))
+  slice         : Term Σ Γ Δ (array t (n ℕ.+ m)) → Term Σ Γ Δ (fin (suc n)) → Term Σ Γ Δ (array t m)
+  cut           : Term Σ Γ Δ (array t (n ℕ.+ m)) → Term Σ Γ Δ (fin (suc n)) → Term Σ Γ Δ (array t n)
+  cast          : .(eq : m ≡ n) → Term Σ Γ Δ (array t m) → Term Σ Γ Δ (array t n)
+  -_            : ⦃ IsNumeric t ⦄ → Term Σ Γ Δ t → Term Σ Γ Δ t
+  _+_           : ⦃ isNum₁ : IsNumeric t₁ ⦄ → ⦃ isNum₂ : IsNumeric t₂ ⦄ → Term Σ Γ Δ t₁ → Term Σ Γ Δ t₂ → Term Σ Γ Δ (isNum₁ +ᵗ isNum₂)
+  _*_           : ⦃ isNum₁ : IsNumeric t₁ ⦄ → ⦃ isNum₂ : IsNumeric t₂ ⦄ → Term Σ Γ Δ t₁ → Term Σ Γ Δ t₂ → Term Σ Γ Δ (isNum₁ +ᵗ isNum₂)
+  _^_           : ⦃ IsNumeric t ⦄ → Term Σ Γ Δ t → ℕ → Term Σ Γ Δ t
+  _>>_          : Term Σ Γ Δ int → (n : ℕ) → Term Σ Γ Δ int
+  rnd           : Term Σ Γ Δ real → Term Σ Γ Δ int
+  fin           : ∀ {ms} (f : literalTypes (map fin ms) → Fin n) → Term Σ Γ Δ (tuple {n = o} (map fin ms)) → Term Σ Γ Δ (fin n)
+  asInt         : Term Σ Γ Δ (fin n) → Term Σ Γ Δ int
+  nil           : Term Σ Γ Δ (tuple [])
+  cons          : Term Σ Γ Δ t → Term Σ Γ Δ (tuple ts) → Term Σ Γ Δ (tuple (t ∷ ts))
+  head          : Term Σ Γ Δ (tuple (t ∷ ts)) → Term Σ Γ Δ t
+  tail          : Term Σ Γ Δ (tuple (t ∷ ts)) → Term Σ Γ Δ (tuple ts)
+  if_then_else_ : Term Σ Γ Δ bool → Term Σ Γ Δ t → Term Σ Γ Δ t → Term Σ Γ Δ t
+
+↓_ : Expression Σ Γ t → Term Σ Γ Δ t
+↓ e = go (Flatten.expr e) (Flatten.expr-depth e)
   where
-  reasoning = slicedSize _ m i
-  k = proj₁ reasoning
-  n≡i+k = sym (proj₂ (proj₂ reasoning))
-  low = take′ t (Fin.toℕ i) (cast′ t n≡i+k y)
-  high = drop′ t (Fin.toℕ i) (cast′ t n≡i+k y)
-  eq = sym (proj₁ (proj₂ reasoning))
-
-splice : ∀ t → Term Σ Γ Δ (asType t m) → Term Σ Γ Δ (asType t n) → Term Σ Γ Δ (fin (suc n)) → Term Σ Γ Δ (asType t (n ℕ.+ m))
-splice τ t₁ t₂ t′ = func (λ (x , y , i , _) → splice′ τ x y i) (t₁ ∷ t₂ ∷ t′ ∷ [])
-
--- i of x is 0 of first
-cut′ : ∀ t → ⟦ asType t (n ℕ.+ m) ⟧ₜ → ⟦ fin (suc n) ⟧ₜ → ⟦ asType t m ∷ asType t n ∷ [] ⟧ₜ′
-cut′ {m = m} t x (lift i) = middle , cast′ t i+k≡n (join′ t high low) , _
-  where
-  reasoning = slicedSize _ m i
-  k = proj₁ reasoning
-  i+k≡n = proj₂ (proj₂ reasoning)
-  eq = proj₁ (proj₂ reasoning)
-  low = take′ t (Fin.toℕ i) (cast′ t eq x)
-  middle = take′ t m (drop′ t (Fin.toℕ i) (cast′ t eq x))
-  high = drop′ t m (drop′ t (Fin.toℕ i) (cast′ t eq x))
-
-cut : ∀ t → Term Σ Γ Δ (asType t (n ℕ.+ m)) → Term Σ Γ Δ (fin (suc n)) → Term Σ Γ Δ (tuple _ (asType t m ∷ asType t n ∷ []))
-cut τ t t′ = func₂ (cut′ τ) t t′
-
-flatten : ∀ {ms : Vec ℕ n} → ⟦ Vec.map fin ms ⟧ₜ′ → All Fin ms
-flatten {ms = []}     _             = []
-flatten {ms = _ ∷ ms} (lift x , xs) = x ∷ flatten xs
-
-𝒦 : Literal t → Term Σ Γ Δ t
-𝒦 (x ′b) = func₀ (lift x)
-𝒦 (x ′i) = func₀ (lift (x ℤ′.×′ 1ℤ))
-𝒦 (x ′f) = func₀ (lift x)
-𝒦 (x ′r) = func₀ (lift (x ℝ′.×′ 1ℝ))
-𝒦 (x ′x) = func₀ (lift (Bool.if x then 1𝔹 else 0𝔹))
-𝒦 ([] ′xs) = func₀ []
-𝒦 ((x ∷ xs) ′xs) = func₂ (flip Vec._∷ʳ_) (𝒦 (x ′x)) (𝒦 (xs ′xs))
-𝒦 (x ′a) = func₁ Vec.replicate (𝒦 x)
-
-module _ (2≉0 : 2≉0) where
-  ℰ : Code.Expression Σ Γ t → Term Σ Γ Δ t
-  ℰ e = (uncurry helper) (M.elimFunctions e)
-    where
-    1+m⊔n≡1+k : ∀ m n → ∃ λ k → suc m ℕ.⊔ n ≡ suc k
-    1+m⊔n≡1+k m 0       = m , refl
-    1+m⊔n≡1+k m (suc n) = m ℕ.⊔ n , refl
-
-    pull-0₂ : ∀ {x y} → x ℕ.⊔ y ≡ 0 → x ≡ 0
-    pull-0₂ {0} {0}     refl = refl
-    pull-0₂ {0} {suc y} ()
-
-    pull-0₃ : ∀ {x y z} → x ℕ.⊔ y ℕ.⊔ z ≡ 0 → x ≡ 0
-    pull-0₃ {0}     {0}     {0} refl = refl
-    pull-0₃ {0}     {suc y} {0}     ()
-    pull-0₃ {suc x} {0}     {0}     ()
-    pull-0₃ {suc x} {0}     {suc z} ()
-
-    pull-1₃ : ∀ x {y z} → x ℕ.⊔ y ℕ.⊔ z ≡ 0 → y ≡ 0
-    pull-1₃ 0       {0}     {0}     refl = refl
-    pull-1₃ 0       {suc y} {0}     ()
-    pull-1₃ (suc x) {0}     {0}     ()
-    pull-1₃ (suc x) {0}     {suc z} ()
-
-    pull-last : ∀ {x y} → x ℕ.⊔ y ≡ 0 → y ≡ 0
-    pull-last {0}     {0} refl = refl
-    pull-last {suc x} {0} ()
-
-    helper : ∀ (e : Code.Expression Σ Γ t) → M.callDepth e ≡ 0 → Term Σ Γ Δ t
-    helper (Code.lit x) eq = 𝒦 x
-    helper (Code.state i) eq = state i
-    helper (Code.var i) eq = var i
-    helper (Code.abort e) eq = func₁ (λ ()) (helper e eq)
-    helper (Code._≟_ {hasEquality = hasEq} e e₁) eq = [ toWitness hasEq ][ helper e (pull-0₂ eq) ≟ helper e₁ (pull-last eq) ]
-    helper (Code._<?_ {isNumeric = isNum} e e₁) eq = [ toWitness isNum ][ helper e (pull-0₂ eq) <? helper e₁ (pull-last eq) ]
-    helper (Code.inv e) eq = func₁ (lift ∘ Bool.not ∘ lower) (helper e eq)
-    helper (e Code.&& e₁) eq = func₂ (λ (lift x) (lift y) → lift (x Bool.∧ y)) (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (e Code.|| e₁) eq = func₂ (λ (lift x) (lift y) → lift (x Bool.∨ y)) (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (Code.not e) eq = func₁ (Vec.map (lift ∘ 𝔹.¬_ ∘ lower)) (helper e eq)
-    helper (e Code.and e₁) eq = func₂ (λ xs ys → Vec.zipWith (λ (lift x) (lift y) → lift (x 𝔹.∧ y)) xs ys) (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (e Code.or e₁) eq = func₂ (λ xs ys → Vec.zipWith (λ (lift x) (lift y) → lift (x 𝔹.∨ y)) xs ys) (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (Code.[_] {t = t} e) eq = [ t ][ helper e eq ]
-    helper (Code.unbox {t = t} e) eq = unbox t (helper e eq)
-    helper (Code.splice {t = t} e e₁ e₂) eq = splice t (helper e (pull-0₃ eq)) (helper e₁ (pull-1₃ (M.callDepth e) eq)) (helper e₂ (pull-last eq))
-    helper (Code.cut {t = t} e e₁) eq = cut t (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (Code.cast {t = t} i≡j e) eq = cast t i≡j (helper e eq)
-    helper (Code.-_ {isNumeric = isNum} e) eq = [ toWitness isNum ][- helper e eq ]
-    helper (Code._+_ {isNumeric₁ = isNum₁} {isNumeric₂ = isNum₂} e e₁) eq = [ _ , _ , isNum₁ , isNum₂ ][ helper e (pull-0₂ eq) + helper e₁ (pull-last eq) ]
-    helper (Code._*_ {isNumeric₁ = isNum₁} {isNumeric₂ = isNum₂} e e₁) eq = [ _ , _ , isNum₁ , isNum₂ ][ helper e (pull-0₂ eq) * helper e₁ (pull-last eq) ]
-    helper (Code._^_ {isNumeric = isNum} e y) eq = [ toWitness isNum ][ helper e eq ^ y ]
-    helper (e Code.>> n) eq = [ 2≉0 ][ helper e eq >> n ]
-    helper (Code.rnd e) eq = func₁ (lift ∘ ⌊_⌋ ∘ lower) (helper e eq)
-    helper (Code.fin f e) eq = func₁ (lift ∘ f ∘ flatten) (helper e eq)
-    helper (Code.asInt e) eq = func₁ (lift ∘ (ℤ′._×′ 1ℤ) ∘ Fin.toℕ ∘ lower) (helper e eq)
-    helper Code.nil eq = func₀ _
-    helper (Code.cons e e₁) eq = func₂ _,_ (helper e (pull-0₂ eq)) (helper e₁ (pull-last eq))
-    helper (Code.head e) eq = func₁ proj₁ (helper e eq)
-    helper (Code.tail e) eq = func₁ proj₂ (helper e eq)
-    helper (Code.call f es) eq = contradiction (trans (sym eq) (proj₂ (1+m⊔n≡1+k (M.funCallDepth f) (M.callDepth′ es)))) ℕₚ.0≢1+n
-    helper (Code.if e then e₁ else e₂) eq = func (λ (lift b , x , x₁ , _) → Bool.if b then x else x₁) (helper e (pull-0₃ eq) ∷ helper e₁ (pull-1₃ (M.callDepth e) eq) ∷ helper e₂ (pull-last eq) ∷ [])
-
-  ℰ′ : All (Code.Expression Σ Γ) ts → All (Term Σ Γ Δ) ts
-  ℰ′ []       = []
-  ℰ′ (e ∷ es) = ℰ e ∷ ℰ′ es
-
-  subst : Term Σ Γ Δ t → {e : Code.Expression Σ Γ t′} → Code.CanAssign Σ e → Term Σ Γ Δ t′ → Term Σ Γ Δ t
-  subst t (Code.state i) t′ = substState t i t′
-  subst t (Code.var i) t′ = substVar t i t′
-  subst t (Code.abort e) t′ = func₁ (λ ()) (ℰ e)
-  subst t (Code.[_] {t = τ} ref) t′ = subst t ref (unbox τ t′)
-  subst t (Code.unbox {t = τ} ref) t′ = subst t ref [ τ ][ t′ ]
-  subst t (Code.splice {t = τ} ref ref₁ e₃) t′ = subst (subst t ref (func₁ proj₁ (cut τ t′ (ℰ e₃)))) ref₁ (func₁ (proj₁ ∘ proj₂) (cut τ t′ (ℰ e₃)))
-  subst t (Code.cut {t = τ} ref e₂) t′ = subst t ref (splice τ (func₁ proj₁ t′) (func₁ (proj₁ ∘ proj₂) t′) (ℰ e₂))
-  subst t (Code.cast {t = τ} eq ref) t′ = subst t ref (cast τ (sym eq) t′)
-  subst t Code.nil t′ = t
-  subst t (Code.cons ref ref₁) t′ = subst (subst t ref (func₁ proj₁ t′)) ref₁ (func₁ proj₂ t′)
-  subst t (Code.head {e = e} ref) t′ = subst t ref (func₂ _,_ t′ (func₁ proj₂ (ℰ e)))
-  subst t (Code.tail {t = τ} {e = e} ref) t′ = subst t ref (func₂ {t₁ = τ} _,_ (func₁ proj₁ (ℰ e)) t′)
-
-⟦_⟧ : Term Σ Γ Δ t → ⟦ Σ ⟧ₜ′ → ⟦ Γ ⟧ₜ′ → ⟦ Δ ⟧ₜ′ → ⟦ t ⟧ₜ
-⟦_⟧′ : ∀ {ts} → All (Term Σ Γ Δ) {n} ts → ⟦ Σ ⟧ₜ′ → ⟦ Γ ⟧ₜ′ → ⟦ Δ ⟧ₜ′ → ⟦ ts ⟧ₜ′
-
-⟦ state i ⟧ σ γ δ = fetch i σ
-⟦ var i ⟧ σ γ δ = fetch i γ
-⟦ meta i ⟧ σ γ δ = fetch i δ
-⟦ func f ts ⟧ σ γ δ = f (⟦ ts ⟧′ σ γ δ)
-
-⟦ [] ⟧′     σ γ δ = _
-⟦ t ∷ ts ⟧′ σ γ δ = ⟦ t ⟧ σ γ δ , ⟦ ts ⟧′ σ γ δ
+  ⊔-inj : ∀ i xs → ⨆[ n ] xs ≡ 0 → Vecᵣ.lookup i xs ≡ 0
+  ⊔-inj i xs eq = ℕₚ.n≤0⇒n≡0 (ℕₚ.≤-trans (lookup-⨆-≤ i xs) (ℕₚ.≤-reflexive eq))
+
+  go : ∀ (e : Expression Σ Γ t) → CallDepth.expr e ≡ 0 → Term Σ Γ Δ t
+  go (lit {t} x)            ≡0 = lit (Κ[ t ] x)
+  go (state i)              ≡0 = state i
+  go (var i)                ≡0 = var i
+  go (e ≟ e₁)               ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) ≟ go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (e <? e₁)              ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) <? go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (inv e)                ≡0 = inv (go e ≡0)
+  go (e && e₁)              ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) && go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (e || e₁)              ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) || go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (not e)                ≡0 = not (go e ≡0)
+  go (e and e₁)             ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) and go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (e or e₁)              ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) or go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go [ e ]                  ≡0 = [ go e ≡0 ]
+  go (unbox e)              ≡0 = unbox (go e ≡0)
+  go (merge e e₁ e₂)        ≡0 = merge (go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0)) (go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0)) (go e₂ (⊔-inj 2F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0))
+  go (slice e e₁)           ≡0 = slice (go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0)) (go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0))
+  go (cut e e₁)             ≡0 = cut (go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0)) (go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0))
+  go (cast eq e)            ≡0 = cast eq (go e ≡0)
+  go (- e)                  ≡0 = - go e ≡0
+  go (e + e₁)               ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) + go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (e * e₁)               ≡0 = go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0) * go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0)
+  go (e ^ x)                ≡0 = go e ≡0 ^ x
+  go (e >> n)               ≡0 = go e ≡0 >> n
+  go (rnd e)                ≡0 = rnd (go e ≡0)
+  go (fin f e)              ≡0 = fin f (go e ≡0)
+  go (asInt e)              ≡0 = asInt (go e ≡0)
+  go nil                    ≡0 = nil
+  go (cons e e₁)            ≡0 = cons (go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁) ≡0)) (go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁) ≡0))
+  go (head e)               ≡0 = head (go e ≡0)
+  go (tail e)               ≡0 = tail (go e ≡0)
+  go (call f es)            ≡0 = ⊥-elim (ℕₚ.>⇒≢ (CallDepth.call>0 f es) ≡0)
+  go (if e then e₁ else e₂) ≡0 = if go e (⊔-inj 0F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0) then go e₁ (⊔-inj 1F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0) else go e₂ (⊔-inj 2F (CallDepth.expr e , CallDepth.expr e₁ , CallDepth.expr e₂) ≡0)
+
+module Cast where
+  type : t ≡ t′ → Term Σ Γ Δ t → Term Σ Γ Δ t′
+  type refl = id
+
+module State where
+  subst : ∀ i → Term Σ Γ Δ t → Term Σ Γ Δ (lookup Σ i) → Term Σ Γ Δ t
+  subst i (lit x)                e′ = lit x
+  subst i (state j)              e′ with i Fin.≟ j
+  ...                              | yes refl = e′
+  ...                              | no i≢j   = state j
+  subst i (var j)                e′ = var j
+  subst i (meta j)               e′ = meta j
+  subst i (e ≟ e₁)               e′ = subst i e e′ ≟ subst i e₁ e′
+  subst i (e <? e₁)              e′ = subst i e e′ <? subst i e₁ e′
+  subst i (inv e)                e′ = inv (subst i e e′)
+  subst i (e && e₁)              e′ = subst i e e′ && subst i e₁ e′
+  subst i (e || e₁)              e′ = subst i e e′ || subst i e₁ e′
+  subst i (not e)                e′ = not (subst i e e′)
+  subst i (e and e₁)             e′ = subst i e e′ and subst i e₁ e′
+  subst i (e or e₁)              e′ = subst i e e′ or subst i e₁ e′
+  subst i [ e ]                  e′ = [ subst i e e′ ]
+  subst i (unbox e)              e′ = unbox (subst i e e′)
+  subst i (merge e e₁ e₂)        e′ = merge (subst i e e′) (subst i e₁ e′) (subst i e₂ e′)
+  subst i (slice e e₁)           e′ = slice (subst i e e′) (subst i e₁ e′)
+  subst i (cut e e₁)             e′ = cut (subst i e e′) (subst i e₁ e′)
+  subst i (cast eq e)            e′ = cast eq (subst i e e′)
+  subst i (- e)                  e′ = - subst i e e′
+  subst i (e + e₁)               e′ = subst i e e′ + subst i e₁ e′
+  subst i (e * e₁)               e′ = subst i e e′ * subst i e₁ e′
+  subst i (e ^ x)                e′ = subst i e e′ ^ x
+  subst i (e >> n)               e′ = subst i e e′ >> n
+  subst i (rnd e)                e′ = rnd (subst i e e′)
+  subst i (fin f e)              e′ = fin f (subst i e e′)
+  subst i (asInt e)              e′ = asInt (subst i e e′)
+  subst i nil                    e′ = nil
+  subst i (cons e e₁)            e′ = cons (subst i e e′) (subst i e₁ e′)
+  subst i (head e)               e′ = head (subst i e e′)
+  subst i (tail e)               e′ = tail (subst i e e′)
+  subst i (if e then e₁ else e₂) e′ = if subst i e e′ then subst i e₁ e′ else subst i e₂ e′
+
+module Var {Γ : Vec Type o} where
+  weaken : ∀ i → Term Σ Γ Δ t → Term Σ (insert Γ i t′) Δ t
+  weaken i (lit x)                = lit x
+  weaken i (state j)              = state j
+  weaken i (var j)                = Cast.type (Vecₚ.insert-punchIn _ i _ j) (var (Fin.punchIn i j))
+  weaken i (meta j)               = meta j
+  weaken i (e ≟ e₁)               = weaken i e ≟ weaken i e₁
+  weaken i (e <? e₁)              = weaken i e <? weaken i e₁
+  weaken i (inv e)                = inv (weaken i e)
+  weaken i (e && e₁)              = weaken i e && weaken i e₁
+  weaken i (e || e₁)              = weaken i e || weaken i e₁
+  weaken i (not e)                = not (weaken i e)
+  weaken i (e and e₁)             = weaken i e and weaken i e₁
+  weaken i (e or e₁)              = weaken i e or weaken i e₁
+  weaken i [ e ]                  = [ weaken i e ]
+  weaken i (unbox e)              = unbox (weaken i e)
+  weaken i (merge e e₁ e₂)        = merge (weaken i e) (weaken i e₁) (weaken i e₂)
+  weaken i (slice e e₁)           = slice (weaken i e) (weaken i e₁)
+  weaken i (cut e e₁)             = cut (weaken i e) (weaken i e₁)
+  weaken i (cast eq e)            = cast eq (weaken i e)
+  weaken i (- e)                  = - weaken i e
+  weaken i (e + e₁)               = weaken i e + weaken i e₁
+  weaken i (e * e₁)               = weaken i e * weaken i e₁
+  weaken i (e ^ x)                = weaken i e ^ x
+  weaken i (e >> n)               = weaken i e >> n
+  weaken i (rnd e)                = rnd (weaken i e)
+  weaken i (fin f e)              = fin f (weaken i e)
+  weaken i (asInt e)              = asInt (weaken i e)
+  weaken i nil                    = nil
+  weaken i (cons e e₁)            = cons (weaken i e) (weaken i e₁)
+  weaken i (head e)               = head (weaken i e)
+  weaken i (tail e)               = tail (weaken i e)
+  weaken i (if e then e₁ else e₂) = if weaken i e then weaken i e₁ else weaken i e₂
+
+  weakenAll : Term Σ [] Δ t → Term Σ Γ Δ t
+  weakenAll (lit x)                = lit x
+  weakenAll (state j)              = state j
+  weakenAll (meta j)               = meta j
+  weakenAll (e ≟ e₁)               = weakenAll e ≟ weakenAll e₁
+  weakenAll (e <? e₁)              = weakenAll e <? weakenAll e₁
+  weakenAll (inv e)                = inv (weakenAll e)
+  weakenAll (e && e₁)              = weakenAll e && weakenAll e₁
+  weakenAll (e || e₁)              = weakenAll e || weakenAll e₁
+  weakenAll (not e)                = not (weakenAll e)
+  weakenAll (e and e₁)             = weakenAll e and weakenAll e₁
+  weakenAll (e or e₁)              = weakenAll e or weakenAll e₁
+  weakenAll [ e ]                  = [ weakenAll e ]
+  weakenAll (unbox e)              = unbox (weakenAll e)
+  weakenAll (merge e e₁ e₂)        = merge (weakenAll e) (weakenAll e₁) (weakenAll e₂)
+  weakenAll (slice e e₁)           = slice (weakenAll e) (weakenAll e₁)
+  weakenAll (cut e e₁)             = cut (weakenAll e) (weakenAll e₁)
+  weakenAll (cast eq e)            = cast eq (weakenAll e)
+  weakenAll (- e)                  = - weakenAll e
+  weakenAll (e + e₁)               = weakenAll e + weakenAll e₁
+  weakenAll (e * e₁)               = weakenAll e * weakenAll e₁
+  weakenAll (e ^ x)                = weakenAll e ^ x
+  weakenAll (e >> n)               = weakenAll e >> n
+  weakenAll (rnd e)                = rnd (weakenAll e)
+  weakenAll (fin f e)              = fin f (weakenAll e)
+  weakenAll (asInt e)              = asInt (weakenAll e)
+  weakenAll nil                    = nil
+  weakenAll (cons e e₁)            = cons (weakenAll e) (weakenAll e₁)
+  weakenAll (head e)               = head (weakenAll e)
+  weakenAll (tail e)               = tail (weakenAll e)
+  weakenAll (if e then e₁ else e₂) = if weakenAll e then weakenAll e₁ else weakenAll e₂
+
+  inject : ∀ (ts : Vec Type n) → Term Σ Γ Δ t → Term Σ (Γ ++ ts) Δ t
+  inject ts (lit x)                = lit x
+  inject ts (state j)              = state j
+  inject ts (var j)                = Cast.type (Vecₚ.lookup-++ˡ Γ ts j) (var (Fin.inject+ _ j))
+  inject ts (meta j)               = meta j
+  inject ts (e ≟ e₁)               = inject ts e ≟ inject ts e₁
+  inject ts (e <? e₁)              = inject ts e <? inject ts e₁
+  inject ts (inv e)                = inv (inject ts e)
+  inject ts (e && e₁)              = inject ts e && inject ts e₁
+  inject ts (e || e₁)              = inject ts e || inject ts e₁
+  inject ts (not e)                = not (inject ts e)
+  inject ts (e and e₁)             = inject ts e and inject ts e₁
+  inject ts (e or e₁)              = inject ts e or inject ts e₁
+  inject ts [ e ]                  = [ inject ts e ]
+  inject ts (unbox e)              = unbox (inject ts e)
+  inject ts (merge e e₁ e₂)        = merge (inject ts e) (inject ts e₁) (inject ts e₂)
+  inject ts (slice e e₁)           = slice (inject ts e) (inject ts e₁)
+  inject ts (cut e e₁)             = cut (inject ts e) (inject ts e₁)
+  inject ts (cast eq e)            = cast eq (inject ts e)
+  inject ts (- e)                  = - inject ts e
+  inject ts (e + e₁)               = inject ts e + inject ts e₁
+  inject ts (e * e₁)               = inject ts e * inject ts e₁
+  inject ts (e ^ x)                = inject ts e ^ x
+  inject ts (e >> n)               = inject ts e >> n
+  inject ts (rnd e)                = rnd (inject ts e)
+  inject ts (fin f e)              = fin f (inject ts e)
+  inject ts (asInt e)              = asInt (inject ts e)
+  inject ts nil                    = nil
+  inject ts (cons e e₁)            = cons (inject ts e) (inject ts e₁)
+  inject ts (head e)               = head (inject ts e)
+  inject ts (tail e)               = tail (inject ts e)
+  inject ts (if e then e₁ else e₂) = if inject ts e then inject ts e₁ else inject ts e₂
+
+  raise : ∀ (ts : Vec Type n) → Term Σ Γ Δ t → Term Σ (ts ++ Γ) Δ t
+  raise ts (lit x)                = lit x
+  raise ts (state j)              = state j
+  raise ts (var j)                = Cast.type (Vecₚ.lookup-++ʳ ts Γ j) (var (Fin.raise _ j))
+  raise ts (meta j)               = meta j
+  raise ts (e ≟ e₁)               = raise ts e ≟ raise ts e₁
+  raise ts (e <? e₁)              = raise ts e <? raise ts e₁
+  raise ts (inv e)                = inv (raise ts e)
+  raise ts (e && e₁)              = raise ts e && raise ts e₁
+  raise ts (e || e₁)              = raise ts e || raise ts e₁
+  raise ts (not e)                = not (raise ts e)
+  raise ts (e and e₁)             = raise ts e and raise ts e₁
+  raise ts (e or e₁)              = raise ts e or raise ts e₁
+  raise ts [ e ]                  = [ raise ts e ]
+  raise ts (unbox e)              = unbox (raise ts e)
+  raise ts (merge e e₁ e₂)        = merge (raise ts e) (raise ts e₁) (raise ts e₂)
+  raise ts (slice e e₁)           = slice (raise ts e) (raise ts e₁)
+  raise ts (cut e e₁)             = cut (raise ts e) (raise ts e₁)
+  raise ts (cast eq e)            = cast eq (raise ts e)
+  raise ts (- e)                  = - raise ts e
+  raise ts (e + e₁)               = raise ts e + raise ts e₁
+  raise ts (e * e₁)               = raise ts e * raise ts e₁
+  raise ts (e ^ x)                = raise ts e ^ x
+  raise ts (e >> n)               = raise ts e >> n
+  raise ts (rnd e)                = rnd (raise ts e)
+  raise ts (fin f e)              = fin f (raise ts e)
+  raise ts (asInt e)              = asInt (raise ts e)
+  raise ts nil                    = nil
+  raise ts (cons e e₁)            = cons (raise ts e) (raise ts e₁)
+  raise ts (head e)               = head (raise ts e)
+  raise ts (tail e)               = tail (raise ts e)
+  raise ts (if e then e₁ else e₂) = if raise ts e then raise ts e₁ else raise ts e₂
+
+  elim : ∀ i → Term Σ (insert Γ i t′) Δ t → Term Σ Γ Δ t′ → Term Σ Γ Δ t
+  elim i (lit x)                e′ = lit x
+  elim i (state j)              e′ = state j
+  elim i (var j)                e′ with i Fin.≟ j
+  ...                              | yes refl = Cast.type (sym (Vecₚ.insert-lookup Γ i _)) e′
+  ...                              | no i≢j   = Cast.type (punchOut-insert Γ i≢j _) (var (Fin.punchOut i≢j))
+  elim i (meta j)               e′ = meta j
+  elim i (e ≟ e₁)               e′ = elim i e e′ ≟ elim i e₁ e′
+  elim i (e <? e₁)              e′ = elim i e e′ <? elim i e₁ e′
+  elim i (inv e)                e′ = inv (elim i e e′)
+  elim i (e && e₁)              e′ = elim i e e′ && elim i e₁ e′
+  elim i (e || e₁)              e′ = elim i e e′ || elim i e₁ e′
+  elim i (not e)                e′ = not (elim i e e′)
+  elim i (e and e₁)             e′ = elim i e e′ and elim i e₁ e′
+  elim i (e or e₁)              e′ = elim i e e′ or elim i e₁ e′
+  elim i [ e ]                  e′ = [ elim i e e′ ]
+  elim i (unbox e)              e′ = unbox (elim i e e′)
+  elim i (merge e e₁ e₂)        e′ = merge (elim i e e′) (elim i e₁ e′) (elim i e₂ e′)
+  elim i (slice e e₁)           e′ = slice (elim i e e′) (elim i e₁ e′)
+  elim i (cut e e₁)             e′ = cut (elim i e e′) (elim i e₁ e′)
+  elim i (cast eq e)            e′ = cast eq (elim i e e′)
+  elim i (- e)                  e′ = - elim i e e′
+  elim i (e + e₁)               e′ = elim i e e′ + elim i e₁ e′
+  elim i (e * e₁)               e′ = elim i e e′ * elim i e₁ e′
+  elim i (e ^ x)                e′ = elim i e e′ ^ x
+  elim i (e >> n)               e′ = elim i e e′ >> n
+  elim i (rnd e)                e′ = rnd (elim i e e′)
+  elim i (fin f e)              e′ = fin f (elim i e e′)
+  elim i (asInt e)              e′ = asInt (elim i e e′)
+  elim i nil                    e′ = nil
+  elim i (cons e e₁)            e′ = cons (elim i e e′) (elim i e₁ e′)
+  elim i (head e)               e′ = head (elim i e e′)
+  elim i (tail e)               e′ = tail (elim i e e′)
+  elim i (if e then e₁ else e₂) e′ = if elim i e e′ then elim i e₁ e′ else elim i e₂ e′
+
+  elimAll : Term Σ Γ Δ t → All (Term Σ ts Δ) Γ → Term Σ ts Δ t
+  elimAll (lit x)                es = lit x
+  elimAll (state j)              es = state j
+  elimAll (var j)                es = All.lookup j es
+  elimAll (meta j)               es = meta j
+  elimAll (e ≟ e₁)               es = elimAll e es ≟ elimAll e₁ es
+  elimAll (e <? e₁)              es = elimAll e es <? elimAll e₁ es
+  elimAll (inv e)                es = inv (elimAll e es)
+  elimAll (e && e₁)              es = elimAll e es && elimAll e₁ es
+  elimAll (e || e₁)              es = elimAll e es || elimAll e₁ es
+  elimAll (not e)                es = not (elimAll e es)
+  elimAll (e and e₁)             es = elimAll e es and elimAll e₁ es
+  elimAll (e or e₁)              es = elimAll e es or elimAll e₁ es
+  elimAll [ e ]                  es = [ elimAll e es ]
+  elimAll (unbox e)              es = unbox (elimAll e es)
+  elimAll (merge e e₁ e₂)        es = merge (elimAll e es) (elimAll e₁ es) (elimAll e₂ es)
+  elimAll (slice e e₁)           es = slice (elimAll e es) (elimAll e₁ es)
+  elimAll (cut e e₁)             es = cut (elimAll e es) (elimAll e₁ es)
+  elimAll (cast eq e)            es = cast eq (elimAll e es)
+  elimAll (- e)                  es = - elimAll e es
+  elimAll (e + e₁)               es = elimAll e es + elimAll e₁ es
+  elimAll (e * e₁)               es = elimAll e es * elimAll e₁ es
+  elimAll (e ^ x)                es = elimAll e es ^ x
+  elimAll (e >> n)               es = elimAll e es >> n
+  elimAll (rnd e)                es = rnd (elimAll e es)
+  elimAll (fin f e)              es = fin f (elimAll e es)
+  elimAll (asInt e)              es = asInt (elimAll e es)
+  elimAll nil                    es = nil
+  elimAll (cons e e₁)            es = cons (elimAll e es) (elimAll e₁ es)
+  elimAll (head e)               es = head (elimAll e es)
+  elimAll (tail e)               es = tail (elimAll e es)
+  elimAll (if e then e₁ else e₂) es = if elimAll e es then elimAll e₁ es else elimAll e₂ es
+
+  subst : ∀ i → Term Σ Γ Δ t → Term Σ Γ Δ (lookup Γ i) → Term Σ Γ Δ t
+  subst i (lit x)                e′ = lit x
+  subst i (state j)              e′ = state j
+  subst i (var j)                e′ with i Fin.≟ j
+  ...                              | yes refl = e′
+  ...                              | no i≢j   = var j
+  subst i (meta j)               e′ = meta j
+  subst i (e ≟ e₁)               e′ = subst i e e′ ≟ subst i e₁ e′
+  subst i (e <? e₁)              e′ = subst i e e′ <? subst i e₁ e′
+  subst i (inv e)                e′ = inv (subst i e e′)
+  subst i (e && e₁)              e′ = subst i e e′ && subst i e₁ e′
+  subst i (e || e₁)              e′ = subst i e e′ || subst i e₁ e′
+  subst i (not e)                e′ = not (subst i e e′)
+  subst i (e and e₁)             e′ = subst i e e′ and subst i e₁ e′
+  subst i (e or e₁)              e′ = subst i e e′ or subst i e₁ e′
+  subst i [ e ]                  e′ = [ subst i e e′ ]
+  subst i (unbox e)              e′ = unbox (subst i e e′)
+  subst i (merge e e₁ e₂)        e′ = merge (subst i e e′) (subst i e₁ e′) (subst i e₂ e′)
+  subst i (slice e e₁)           e′ = slice (subst i e e′) (subst i e₁ e′)
+  subst i (cut e e₁)             e′ = cut (subst i e e′) (subst i e₁ e′)
+  subst i (cast eq e)            e′ = cast eq (subst i e e′)
+  subst i (- e)                  e′ = - subst i e e′
+  subst i (e + e₁)               e′ = subst i e e′ + subst i e₁ e′
+  subst i (e * e₁)               e′ = subst i e e′ * subst i e₁ e′
+  subst i (e ^ x)                e′ = subst i e e′ ^ x
+  subst i (e >> n)               e′ = subst i e e′ >> n
+  subst i (rnd e)                e′ = rnd (subst i e e′)
+  subst i (fin f e)              e′ = fin f (subst i e e′)
+  subst i (asInt e)              e′ = asInt (subst i e e′)
+  subst i nil                    e′ = nil
+  subst i (cons e e₁)            e′ = cons (subst i e e′) (subst i e₁ e′)
+  subst i (head e)               e′ = head (subst i e e′)
+  subst i (tail e)               e′ = tail (subst i e e′)
+  subst i (if e then e₁ else e₂) e′ = if subst i e e′ then subst i e₁ e′ else subst i e₂ e′
+
+module Meta {Δ : Vec Type o} where
+  weaken : ∀ i → Term Σ Γ Δ t → Term Σ Γ (insert Δ i t′) t
+  weaken i (lit x)                = lit x
+  weaken i (state j)              = state j
+  weaken i (var j)                = var j
+  weaken i (meta j)               = Cast.type (Vecₚ.insert-punchIn _ i _ j) (meta (Fin.punchIn i j))
+  weaken i (e ≟ e₁)               = weaken i e ≟ weaken i e₁
+  weaken i (e <? e₁)              = weaken i e <? weaken i e₁
+  weaken i (inv e)                = inv (weaken i e)
+  weaken i (e && e₁)              = weaken i e && weaken i e₁
+  weaken i (e || e₁)              = weaken i e || weaken i e₁
+  weaken i (not e)                = not (weaken i e)
+  weaken i (e and e₁)             = weaken i e and weaken i e₁
+  weaken i (e or e₁)              = weaken i e or weaken i e₁
+  weaken i [ e ]                  = [ weaken i e ]
+  weaken i (unbox e)              = unbox (weaken i e)
+  weaken i (merge e e₁ e₂)        = merge (weaken i e) (weaken i e₁) (weaken i e₂)
+  weaken i (slice e e₁)           = slice (weaken i e) (weaken i e₁)
+  weaken i (cut e e₁)             = cut (weaken i e) (weaken i e₁)
+  weaken i (cast eq e)            = cast eq (weaken i e)
+  weaken i (- e)                  = - weaken i e
+  weaken i (e + e₁)               = weaken i e + weaken i e₁
+  weaken i (e * e₁)               = weaken i e * weaken i e₁
+  weaken i (e ^ x)                = weaken i e ^ x
+  weaken i (e >> n)               = weaken i e >> n
+  weaken i (rnd e)                = rnd (weaken i e)
+  weaken i (fin f e)              = fin f (weaken i e)
+  weaken i (asInt e)              = asInt (weaken i e)
+  weaken i nil                    = nil
+  weaken i (cons e e₁)            = cons (weaken i e) (weaken i e₁)
+  weaken i (head e)               = head (weaken i e)
+  weaken i (tail e)               = tail (weaken i e)
+  weaken i (if e then e₁ else e₂) = if weaken i e then weaken i e₁ else weaken i e₂
+
+  elim : ∀ i → Term Σ Γ (insert Δ i t′) t → Term Σ Γ Δ t′ → Term Σ Γ Δ t
+  elim i (lit x)                e′ = lit x
+  elim i (state j)              e′ = state j
+  elim i (var j)                e′ = var j
+  elim i (meta j)               e′ with i Fin.≟ j
+  ...                              | yes refl = Cast.type (sym (Vecₚ.insert-lookup Δ i _)) e′
+  ...                              | no i≢j   = Cast.type (punchOut-insert Δ i≢j _) (meta (Fin.punchOut i≢j))
+  elim i (e ≟ e₁)               e′ = elim i e e′ ≟ elim i e₁ e′
+  elim i (e <? e₁)              e′ = elim i e e′ <? elim i e₁ e′
+  elim i (inv e)                e′ = inv (elim i e e′)
+  elim i (e && e₁)              e′ = elim i e e′ && elim i e₁ e′
+  elim i (e || e₁)              e′ = elim i e e′ || elim i e₁ e′
+  elim i (not e)                e′ = not (elim i e e′)
+  elim i (e and e₁)             e′ = elim i e e′ and elim i e₁ e′
+  elim i (e or e₁)              e′ = elim i e e′ or elim i e₁ e′
+  elim i [ e ]                  e′ = [ elim i e e′ ]
+  elim i (unbox e)              e′ = unbox (elim i e e′)
+  elim i (merge e e₁ e₂)        e′ = merge (elim i e e′) (elim i e₁ e′) (elim i e₂ e′)
+  elim i (slice e e₁)           e′ = slice (elim i e e′) (elim i e₁ e′)
+  elim i (cut e e₁)             e′ = cut (elim i e e′) (elim i e₁ e′)
+  elim i (cast eq e)            e′ = cast eq (elim i e e′)
+  elim i (- e)                  e′ = - elim i e e′
+  elim i (e + e₁)               e′ = elim i e e′ + elim i e₁ e′
+  elim i (e * e₁)               e′ = elim i e e′ * elim i e₁ e′
+  elim i (e ^ x)                e′ = elim i e e′ ^ x
+  elim i (e >> n)               e′ = elim i e e′ >> n
+  elim i (rnd e)                e′ = rnd (elim i e e′)
+  elim i (fin f e)              e′ = fin f (elim i e e′)
+  elim i (asInt e)              e′ = asInt (elim i e e′)
+  elim i nil                    e′ = nil
+  elim i (cons e e₁)            e′ = cons (elim i e e′) (elim i e₁ e′)
+  elim i (head e)               e′ = head (elim i e e′)
+  elim i (tail e)               e′ = tail (elim i e e′)
+  elim i (if e then e₁ else e₂) e′ = if elim i e e′ then elim i e₁ e′ else elim i e₂ e′
+
+subst : Term Σ Γ Δ t → Reference Σ Γ t′ → Term Σ Γ Δ t′ → Term Σ Γ Δ t
+subst e (state i)          val = State.subst i e val
+subst e (var i)            val = Var.subst i e val
+subst e [ ref ]            val = subst e ref (unbox val)
+subst e (unbox ref)        val = subst e ref [ val ]
+subst e (merge ref ref₁ x) val = subst (subst e ref (slice val (↓ x))) ref₁ (cut val (↓ x))
+subst e (slice ref x)      val = subst e ref (merge val (↓ ! cut ref x) (↓ x))
+subst e (cut ref x)        val = subst e ref (merge (↓ ! slice ref x) val (↓ x))
+subst e (cast eq ref)      val = subst e ref (cast (sym eq) val)
+subst e nil                val = e
+subst e (cons ref ref₁)    val = subst (subst e ref (head val)) ref₁ (tail val)
+subst e (head ref)         val = subst e ref (cons val (↓ ! tail ref))
+subst e (tail ref)         val = subst e ref (cons (↓ ! head ref) val)
+
+module Semantics (2≉0 : 2≉0) {Σ : Vec Type i} {Γ : Vec Type j} {Δ : Vec Type k} where
+  ⟦_⟧ : Term Σ Γ Δ t → ⟦ Σ ⟧ₜ′ → ⟦ Γ ⟧ₜ′ → ⟦ Δ ⟧ₜ′ → ⟦ t ⟧ₜ
+  ⟦ lit x ⟧                σ γ δ = x
+  ⟦ state i ⟧              σ γ δ = fetch i Σ σ
+  ⟦ var i ⟧                σ γ δ = fetch i Γ γ
+  ⟦ meta i ⟧               σ γ δ = fetch i Δ δ
+  ⟦ e ≟ e₁ ⟧               σ γ δ = (lift ∘₂ does ∘₂ ≈-dec) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ e <? e₁ ⟧              σ γ δ = (lift ∘₂ does ∘₂ <-dec) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ inv e ⟧                σ γ δ = lift ∘ Bool.not ∘ lower $ ⟦ e ⟧ σ γ δ
+  ⟦ e && e₁ ⟧              σ γ δ = (lift ∘₂ Bool._∧_ on lower) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ e || e₁ ⟧              σ γ δ = (lift ∘₂ Bool._∨_ on lower) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ not e ⟧                σ γ δ = map (lift ∘ 𝔹.¬_ ∘ lower) (⟦ e ⟧ σ γ δ)
+  ⟦ e and e₁ ⟧             σ γ δ = zipWith (lift ∘₂ 𝔹._∧_ on lower) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ e or e₁ ⟧              σ γ δ = zipWith (lift ∘₂ 𝔹._∨_ on lower) (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ [ e ] ⟧                σ γ δ = ⟦ e ⟧ σ γ δ ∷ []
+  ⟦ unbox e ⟧              σ γ δ = Vec.head (⟦ e ⟧ σ γ δ)
+  ⟦ merge e e₁ e₂ ⟧        σ γ δ = mergeVec (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ) (lower (⟦ e₂ ⟧ σ γ δ))
+  ⟦ slice e e₁ ⟧           σ γ δ = sliceVec (⟦ e ⟧ σ γ δ) (lower (⟦ e₁ ⟧ σ γ δ))
+  ⟦ cut e e₁ ⟧             σ γ δ = cutVec (⟦ e ⟧ σ γ δ) (lower (⟦ e₁ ⟧ σ γ δ))
+  ⟦ cast eq e ⟧            σ γ δ = castVec eq (⟦ e ⟧ σ γ δ)
+  ⟦ - e ⟧                  σ γ δ = neg (⟦ e ⟧ σ γ δ)
+  ⟦ e + e₁ ⟧               σ γ δ = add (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ e * e₁ ⟧               σ γ δ = mul (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ e ^ x ⟧                σ γ δ = pow (⟦ e ⟧ σ γ δ) x
+  ⟦ e >> n ⟧               σ γ δ = lift ∘ flip (shift 2≉0) n ∘ lower $ ⟦ e ⟧ σ γ δ
+  ⟦ rnd e ⟧                σ γ δ = lift ∘ ⌊_⌋ ∘ lower $ ⟦ e ⟧ σ γ δ
+  ⟦ fin {ms = ms} f e ⟧    σ γ δ = lift ∘ f ∘ lowerFin ms $ ⟦ e ⟧ σ γ δ
+  ⟦ asInt e ⟧              σ γ δ = lift ∘ 𝕀⇒ℤ ∘ 𝕀.+_ ∘ Fin.toℕ ∘ lower $ ⟦ e ⟧ σ γ δ
+  ⟦ nil ⟧                  σ γ δ = _
+  ⟦ cons {ts = ts} e e₁ ⟧  σ γ δ = cons′ ts (⟦ e ⟧ σ γ δ) (⟦ e₁ ⟧ σ γ δ)
+  ⟦ head {ts = ts} e ⟧     σ γ δ = head′ ts (⟦ e ⟧ σ γ δ)
+  ⟦ tail {ts = ts} e ⟧     σ γ δ = tail′ ts (⟦ e ⟧ σ γ δ)
+  ⟦ if e then e₁ else e₂ ⟧ σ γ δ = Bool.if lower (⟦ e ⟧ σ γ δ) then ⟦ e₁ ⟧ σ γ δ else ⟦ e₂ ⟧ σ γ δ
-- 
cgit v1.2.3