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Some lemmas related to renamings and substitutions #1750

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merged 8 commits into from
Sep 27, 2023
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32 changes: 32 additions & 0 deletions CHANGELOG.md
Original file line number Diff line number Diff line change
Expand Up @@ -1142,6 +1142,38 @@ Other minor changes
cantor-schröder-bernstein : ∀ {f : Fin m → Fin n} {g : Fin n → Fin m} → Injective f → Injective g → m ≡ n
```

* Changed the fixity of `Data.Fin.Substitution.TermSubst._/Var_`.
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* Added new lemmas in `Data.Fin.Substitution.Lemmas.TermLemmas`:
```
map-var≡ :
∀ {m n} {ρ₁ : Sub Fin m n} {ρ₂ : Sub T m n} {f : Fin m → Fin n} →
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(∀ x → lookup ρ₁ x ≡ f x) →
(∀ x → lookup ρ₂ x ≡ T.var (f x)) →
map T.var ρ₁ ≡ ρ₂
wk≡wk :
∀ {n} → map T.var VarSubst.wk ≡ T.wk {n = n}
id≡id :
∀ {n} → map T.var VarSubst.id ≡ T.id {n = n}
sub≡sub :
∀ {n} {x : Fin n} →
map T.var (VarSubst.sub x) ≡ T.sub (T.var x)
↑≡↑ :
∀ {m n} {ρ : Sub Fin m n} →
map T.var (ρ VarSubst.↑) ≡ map T.var ρ T.↑
/Var≡/ :
∀ {m n} {ρ : Sub Fin m n} {t} →
t /Var ρ ≡ t T./ map T.var ρ
sub-renaming-commutes :
∀ {m n t x} {ρ : Sub T m n} →
t /Var VarSubst.sub x T./ ρ ≡
t T./ ρ T.↑ T./ T.sub (lookup ρ x)
sub-commutes-with-renaming :
∀ {m n} {t t′} {ρ : Sub Fin m n} →
t T./ T.sub t′ /Var ρ ≡
t /Var ρ VarSubst.↑ T./ T.sub (t′ /Var ρ)
```

* Added new functions in `Data.Integer.Base`:
```
_^_ : ℤ → ℕ → ℤ
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2 changes: 1 addition & 1 deletion src/Data/Fin/Substitution.agda
Original file line number Diff line number Diff line change
Expand Up @@ -160,7 +160,7 @@ record TermSubst (T : Pred ℕ 0ℓ) : Set₁ where
varLift : Lift Fin T
varLift = record { simple = VarSubst.simple; lift = var }

infix 8 _/Var_
infixl 8 _/Var_

_/Var_ : ∀ {m n} → T m → Sub Fin m n → T n
_/Var_ = app varLift
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66 changes: 66 additions & 0 deletions src/Data/Fin/Substitution/Lemmas.agda
Original file line number Diff line number Diff line change
Expand Up @@ -543,3 +543,69 @@ record TermLemmas (T : ℕ → Set) : Set₁ where
T.weaken t₁ T./ (T.sub t₂) ≡⟨ weaken-∷ t₁ ⟩
t₁ T./ T.id ≡⟨ id-vanishes t₁ ⟩
t₁ ∎

-- Lemmas relating renamings to substitutions.

map-var≡ :
∀ {m n} {ρ₁ : Sub Fin m n} {ρ₂ : Sub T m n} {f : Fin m → Fin n} →
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(∀ x → lookup ρ₁ x ≡ f x) →
(∀ x → lookup ρ₂ x ≡ T.var (f x)) →
map T.var ρ₁ ≡ ρ₂
map-var≡ {ρ₁ = ρ₁} {ρ₂ = ρ₂} {f = f} hyp₁ hyp₂ = extensionality λ x →
lookup (map T.var ρ₁) x ≡⟨ VecProp.lookup-map x _ ρ₁ ⟩
T.var (lookup ρ₁ x) ≡⟨ cong T.var $ hyp₁ x ⟩
T.var (f x) ≡⟨ sym $ hyp₂ x ⟩
lookup ρ₂ x ∎

wk≡wk : ∀ {n} → map T.var VarSubst.wk ≡ T.wk {n = n}
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wk≡wk = map-var≡ VarLemmas.lookup-wk lookup-wk

id≡id : ∀ {n} → map T.var VarSubst.id ≡ T.id {n = n}
id≡id = map-var≡ VarLemmas.lookup-id lookup-id

sub≡sub :
∀ {n} {x : Fin n} →
map T.var (VarSubst.sub x) ≡ T.sub (T.var x)
sub≡sub = cong (_ ∷_) id≡id

↑≡↑ :
∀ {m n} {ρ : Sub Fin m n} →
map T.var (ρ VarSubst.↑) ≡ map T.var ρ T.↑
↑≡↑ {ρ = ρ} = map-var≡
(VarLemmas.lookup-↑⋆ (lookup ρ) (λ _ → refl) 1)
(lookup-↑⋆ (lookup ρ) (λ _ → VecProp.lookup-map _ _ ρ) 1)

/Var≡/ :
∀ {m n} {ρ : Sub Fin m n} {t} →
t /Var ρ ≡ t T./ map T.var ρ
/Var≡/ {ρ = ρ} {t = t} =
/✶-↑✶ (ε ▻ ρ) (ε ▻ map T.var ρ)
(λ k x →
T.var x /Var ρ VarSubst.↑⋆ k ≡⟨ app-var ⟩
T.var (lookup (ρ VarSubst.↑⋆ k) x) ≡⟨ cong T.var $ VarLemmas.lookup-↑⋆ _ (λ _ → refl) k _ ⟩
T.var (lift k (VarSubst._/ ρ) x) ≡⟨ sym $ lookup-↑⋆ _ (λ _ → VecProp.lookup-map _ _ ρ) k _ ⟩
lookup (map T.var ρ T.↑⋆ k) x ≡⟨ sym app-var ⟩
T.var x T./ map T.var ρ T.↑⋆ k ∎)
zero t

sub-renaming-commutes :
∀ {m n t x} {ρ : Sub T m n} →
t /Var VarSubst.sub x T./ ρ ≡
t T./ ρ T.↑ T./ T.sub (lookup ρ x)
sub-renaming-commutes {t = t} {x = x} {ρ = ρ} =
t /Var VarSubst.sub x T./ ρ ≡⟨ cong (T._/ ρ) /Var≡/ ⟩
t T./ map T.var (VarSubst.sub x) T./ ρ ≡⟨ cong (λ ρ′ → t T./ ρ′ T./ ρ) sub≡sub ⟩
t T./ T.sub (T.var x) T./ ρ ≡⟨ sub-commutes _ ⟩
t T./ ρ T.↑ T./ T.sub (T.var x T./ ρ) ≡⟨ cong (λ t′ → t T./ ρ T.↑ T./ T.sub t′) app-var ⟩
t T./ ρ T.↑ T./ T.sub (lookup ρ x) ∎

sub-commutes-with-renaming :
∀ {m n} {t t′} {ρ : Sub Fin m n} →
t T./ T.sub t′ /Var ρ ≡
t /Var ρ VarSubst.↑ T./ T.sub (t′ /Var ρ)
sub-commutes-with-renaming {t = t} {t′ = t′} {ρ = ρ} =
t T./ T.sub t′ /Var ρ ≡⟨ /Var≡/ ⟩
t T./ T.sub t′ T./ map T.var ρ ≡⟨ sub-commutes _ ⟩
t T./ map T.var ρ T.↑ T./ T.sub (t′ T./ map T.var ρ) ≡⟨ sym $ cong (λ ρ′ → t T./ ρ′ T./ T.sub (t′ T./ map T.var ρ)) ↑≡↑ ⟩
t T./ map T.var (ρ VarSubst.↑) T./ T.sub (t′ T./ map T.var ρ) ≡⟨ sym $ cong₂ (λ t ρ → t T./ T.sub ρ) /Var≡/ /Var≡/ ⟩
t /Var ρ VarSubst.↑ T./ T.sub (t′ /Var ρ) ∎