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-rw-r--r--Data/Circuit/Merge.agda341
-rw-r--r--Data/Circuit/Value.agda157
-rw-r--r--Data/Fin/Preimage.agda48
-rw-r--r--Data/Setoid.agda8
-rw-r--r--Data/Subset/Functional.agda162
-rw-r--r--Data/System.agda86
-rw-r--r--Data/System/Values.agda21
-rw-r--r--Data/Vector.agda82
8 files changed, 905 insertions, 0 deletions
diff --git a/Data/Circuit/Merge.agda b/Data/Circuit/Merge.agda
new file mode 100644
index 0000000..82c0d92
--- /dev/null
+++ b/Data/Circuit/Merge.agda
@@ -0,0 +1,341 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Circuit.Merge where
+
+open import Data.Nat.Base using (ℕ)
+open import Data.Fin.Base using (Fin; pinch; punchIn; punchOut)
+open import Data.Fin.Properties using (punchInᵢ≢i; punchIn-punchOut)
+open import Data.Bool.Properties using (if-eta)
+open import Data.Bool using (Bool; if_then_else_)
+open import Data.Circuit.Value using (Value; join; join-comm; join-assoc)
+open import Data.Subset.Functional
+ using
+ ( Subset
+ ; ⁅_⁆ ; ⊥ ; ⁅⁆∘ρ
+ ; foldl ; foldl-cong₁ ; foldl-cong₂
+ ; foldl-[] ; foldl-suc
+ ; foldl-⊥ ; foldl-⁅⁆
+ ; foldl-fusion
+ )
+open import Data.Vector as V using (Vector; head; tail; removeAt)
+open import Data.Fin.Permutation
+ using
+ ( Permutation
+ ; Permutation′
+ ; _⟨$⟩ˡ_ ; _⟨$⟩ʳ_
+ ; inverseˡ ; inverseʳ
+ ; id
+ ; flip
+ ; insert ; remove
+ ; punchIn-permute
+ )
+open import Data.Product using (Σ-syntax; _,_)
+open import Data.Fin.Preimage using (preimage; preimage-cong₁; preimage-cong₂)
+open import Function.Base using (∣_⟩-_; _∘_)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≗_)
+
+open Value using (U)
+open ℕ
+open Fin
+open Bool
+
+_when_ : Value → Bool → Value
+x when b = if b then x else U
+
+opaque
+ merge-with : {A : ℕ} → Value → Vector Value A → Subset A → Value
+ merge-with e v = foldl (∣ join ⟩- v) e
+
+ merge-with-cong : {A : ℕ} {v₁ v₂ : Vector Value A} (e : Value) → v₁ ≗ v₂ → merge-with e v₁ ≗ merge-with e v₂
+ merge-with-cong e v₁≗v₂ = foldl-cong₁ (λ x → ≡.cong (join x) ∘ v₁≗v₂) e
+
+ merge-with-cong₂ : {A : ℕ} (e : Value) (v : Vector Value A) {S₁ S₂ : Subset A} → S₁ ≗ S₂ → merge-with e v S₁ ≡ merge-with e v S₂
+ merge-with-cong₂ e v = foldl-cong₂ (∣ join ⟩- v) e
+
+ merge-with-⊥ : {A : ℕ} (e : Value) (v : Vector Value A) → merge-with e v ⊥ ≡ e
+ merge-with-⊥ e v = foldl-⊥ (∣ join ⟩- v) e
+
+ merge-with-[] : (e : Value) (v : Vector Value 0) (S : Subset 0) → merge-with e v S ≡ e
+ merge-with-[] e v = foldl-[] (∣ join ⟩- v) e
+
+ merge-with-suc
+ : {A : ℕ} (e : Value) (v : Vector Value (suc A)) (S : Subset (suc A))
+ → merge-with e v S
+ ≡ merge-with (if head S then join e (head v) else e) (tail v) (tail S)
+ merge-with-suc e v = foldl-suc (∣ join ⟩- v) e
+
+ merge-with-join
+ : {A : ℕ}
+ (x y : Value)
+ (v : Vector Value A)
+ → merge-with (join x y) v ≗ join x ∘ merge-with y v
+ merge-with-join {A} x y v S = ≡.sym (foldl-fusion (join x) fuse y S)
+ where
+ fuse : (acc : Value) (k : Fin A) → join x (join acc (v k)) ≡ join (join x acc) (v k)
+ fuse acc k = ≡.sym (join-assoc x acc (v k))
+
+ merge-with-⁅⁆ : {A : ℕ} (e : Value) (v : Vector Value A) (x : Fin A) → merge-with e v ⁅ x ⁆ ≡ join e (v x)
+ merge-with-⁅⁆ e v = foldl-⁅⁆ (∣ join ⟩- v) e
+
+merge-with-U : {A : ℕ} (e : Value) (S : Subset A) → merge-with e (λ _ → U) S ≡ e
+merge-with-U {zero} e S = merge-with-[] e (λ _ → U) S
+merge-with-U {suc A} e S = begin
+ merge-with e (λ _ → U) S ≡⟨ merge-with-suc e (λ _ → U) S ⟩
+ merge-with
+ (if head S then join e U else e)
+ (tail (λ _ → U)) (tail S) ≡⟨ ≡.cong (λ h → merge-with (if head S then h else e) _ _) (join-comm e U) ⟩
+ merge-with
+ (if head S then e else e)
+ (tail (λ _ → U)) (tail S) ≡⟨ ≡.cong (λ h → merge-with h (λ _ → U) (tail S)) (if-eta (head S)) ⟩
+ merge-with e (tail (λ _ → U)) (tail S) ≡⟨⟩
+ merge-with e (λ _ → U) (tail S) ≡⟨ merge-with-U e (tail S) ⟩
+ e ∎
+ where
+ open ≡.≡-Reasoning
+
+merge : {A : ℕ} → Vector Value A → Subset A → Value
+merge v = merge-with U v
+
+merge-cong₁ : {A : ℕ} {v₁ v₂ : Vector Value A} → v₁ ≗ v₂ → merge v₁ ≗ merge v₂
+merge-cong₁ = merge-with-cong U
+
+merge-cong₂ : {A : ℕ} (v : Vector Value A) {S₁ S₂ : Subset A} → S₁ ≗ S₂ → merge v S₁ ≡ merge v S₂
+merge-cong₂ = merge-with-cong₂ U
+
+merge-⊥ : {A : ℕ} (v : Vector Value A) → merge v ⊥ ≡ U
+merge-⊥ = merge-with-⊥ U
+
+merge-[] : (v : Vector Value 0) (S : Subset 0) → merge v S ≡ U
+merge-[] = merge-with-[] U
+
+merge-[]₂ : {v₁ v₂ : Vector Value 0} {S₁ S₂ : Subset 0} → merge v₁ S₁ ≡ merge v₂ S₂
+merge-[]₂ {v₁} {v₂} {S₁} {S₂} = ≡.trans (merge-[] v₁ S₁) (≡.sym (merge-[] v₂ S₂))
+
+merge-⁅⁆ : {A : ℕ} (v : Vector Value A) (x : Fin A) → merge v ⁅ x ⁆ ≡ v x
+merge-⁅⁆ = merge-with-⁅⁆ U
+
+join-merge : {A : ℕ} (e : Value) (v : Vector Value A) (S : Subset A) → join e (merge v S) ≡ merge-with e v S
+join-merge e v S = ≡.sym (≡.trans (≡.cong (λ h → merge-with h v S) (join-comm U e)) (merge-with-join e U v S))
+
+merge-suc
+ : {A : ℕ} (v : Vector Value (suc A)) (S : Subset (suc A))
+ → merge v S
+ ≡ merge-with (head v when head S) (tail v) (tail S)
+merge-suc = merge-with-suc U
+
+insert-f0-0
+ : {A B : ℕ}
+ (f : Fin (suc A) → Fin (suc B))
+ → Σ[ ρ ∈ Permutation′ (suc B) ] (ρ ⟨$⟩ʳ (f zero) ≡ zero)
+insert-f0-0 f = insert (f zero) zero id , help
+ where
+ open import Data.Fin using (_≟_)
+ open import Relation.Nullary.Decidable using (yes; no)
+ help : insert (f zero) zero id ⟨$⟩ʳ f zero ≡ zero
+ help with f zero ≟ f zero
+ ... | yes _ = ≡.refl
+ ... | no f0≢f0 with () ← f0≢f0 ≡.refl
+
+merge-removeAt
+ : {A : ℕ}
+ (k : Fin (suc A))
+ (v : Vector Value (suc A))
+ (S : Subset (suc A))
+ → merge v S ≡ join (v k when S k) (merge (removeAt v k) (removeAt S k))
+merge-removeAt {A} zero v S = begin
+ merge-with U v S ≡⟨ merge-suc v S ⟩
+ merge-with (head v when head S) (tail v) (tail S) ≡⟨ join-merge (head v when head S) (tail v) (tail S) ⟨
+ join (head v when head S) (merge-with U (tail v) (tail S)) ∎
+ where
+ open ≡.≡-Reasoning
+merge-removeAt {suc A} (suc k) v S = begin
+ merge-with U v S ≡⟨ merge-suc v S ⟩
+ merge-with v0? (tail v) (tail S) ≡⟨ join-merge _ (tail v) (tail S) ⟨
+ join v0? (merge (tail v) (tail S)) ≡⟨ ≡.cong (join v0?) (merge-removeAt k (tail v) (tail S)) ⟩
+ join v0? (join vk? (merge (tail v-) (tail S-))) ≡⟨ join-assoc (head v when head S) _ _ ⟨
+ join (join v0? vk?) (merge (tail v-) (tail S-)) ≡⟨ ≡.cong (λ h → join h (merge (tail v-) (tail S-))) (join-comm (head v- when head S-) _) ⟩
+ join (join vk? v0?) (merge (tail v-) (tail S-)) ≡⟨ join-assoc (tail v k when tail S k) _ _ ⟩
+ join vk? (join v0? (merge (tail v-) (tail S-))) ≡⟨ ≡.cong (join vk?) (join-merge _ (tail v-) (tail S-)) ⟩
+ join vk? (merge-with v0? (tail v-) (tail S-)) ≡⟨ ≡.cong (join vk?) (merge-suc v- S-) ⟨
+ join vk? (merge v- S-) ∎
+ where
+ v0? vk? : Value
+ v0? = head v when head S
+ vk? = tail v k when tail S k
+ v- : Vector Value (suc A)
+ v- = removeAt v (suc k)
+ S- : Subset (suc A)
+ S- = removeAt S (suc k)
+ open ≡.≡-Reasoning
+
+import Function.Structures as FunctionStructures
+open module FStruct {A B : Set} = FunctionStructures {_} {_} {_} {_} {A} _≡_ {B} _≡_ using (IsInverse)
+open IsInverse using () renaming (inverseˡ to invˡ; inverseʳ to invʳ)
+
+merge-preimage-ρ
+ : {A B : ℕ}
+ → (ρ : Permutation A B)
+ → (v : Vector Value A)
+ (S : Subset B)
+ → merge v (preimage (ρ ⟨$⟩ʳ_) S) ≡ merge (v ∘ (ρ ⟨$⟩ˡ_)) S
+merge-preimage-ρ {zero} {zero} ρ v S = merge-[]₂
+merge-preimage-ρ {zero} {suc B} ρ v S with () ← ρ ⟨$⟩ˡ zero
+merge-preimage-ρ {suc A} {zero} ρ v S with () ← ρ ⟨$⟩ʳ zero
+merge-preimage-ρ {suc A} {suc B} ρ v S = begin
+ merge v (preimage ρʳ S) ≡⟨ merge-removeAt (head ρˡ) v (preimage ρʳ S) ⟩
+ join
+ (head (v ∘ ρˡ) when S (ρʳ (ρˡ zero)))
+ (merge v- [preimageρʳS]-) ≡⟨ ≡.cong (λ h → join h (merge v- [preimageρʳS]-)) ≡vρˡ0? ⟩
+ join vρˡ0? (merge v- [preimageρʳS]-) ≡⟨ ≡.cong (join vρˡ0?) (merge-cong₂ v- preimage-) ⟩
+ join vρˡ0? (merge v- (preimage ρʳ- S-)) ≡⟨ ≡.cong (join vρˡ0?) (merge-preimage-ρ ρ- v- S-) ⟩
+ join vρˡ0? (merge (v- ∘ ρˡ-) S-) ≡⟨ ≡.cong (join vρˡ0?) (merge-cong₁ v∘ρˡ- S-) ⟩
+ join vρˡ0? (merge (tail (v ∘ ρˡ)) S-) ≡⟨ join-merge vρˡ0? (tail (v ∘ ρˡ)) S- ⟩
+ merge-with vρˡ0? (tail (v ∘ ρˡ)) S- ≡⟨ merge-suc (v ∘ ρˡ) S ⟨
+ merge (v ∘ ρˡ) S ∎
+ where
+ ρˡ : Fin (suc B) → Fin (suc A)
+ ρˡ = ρ ⟨$⟩ˡ_
+ ρʳ : Fin (suc A) → Fin (suc B)
+ ρʳ = ρ ⟨$⟩ʳ_
+ ρ- : Permutation A B
+ ρ- = remove (head ρˡ) ρ
+ ρˡ- : Fin B → Fin A
+ ρˡ- = ρ- ⟨$⟩ˡ_
+ ρʳ- : Fin A → Fin B
+ ρʳ- = ρ- ⟨$⟩ʳ_
+ v- : Vector Value A
+ v- = removeAt v (head ρˡ)
+ [preimageρʳS]- : Subset A
+ [preimageρʳS]- = removeAt (preimage ρʳ S) (head ρˡ)
+ S- : Subset B
+ S- = tail S
+ vρˡ0? : Value
+ vρˡ0? = head (v ∘ ρˡ) when head S
+ open ≡.≡-Reasoning
+ ≡vρˡ0?  : head (v ∘ ρˡ) when S (ρʳ (head ρˡ)) ≡ head (v ∘ ρˡ) when head S
+ ≡vρˡ0? = ≡.cong ((head (v ∘ ρˡ) when_) ∘ S) (inverseʳ ρ)
+ v∘ρˡ- : v- ∘ ρˡ- ≗ tail (v ∘ ρˡ)
+ v∘ρˡ- x = begin
+ v- (ρˡ- x) ≡⟨⟩
+ v (punchIn (head ρˡ) (punchOut {A} {head ρˡ} _)) ≡⟨ ≡.cong v (punchIn-punchOut _) ⟩
+ v (ρˡ (punchIn (ρʳ (ρˡ zero)) x)) ≡⟨ ≡.cong (λ h → v (ρˡ (punchIn h x))) (inverseʳ ρ) ⟩
+ v (ρˡ (punchIn zero x)) ≡⟨⟩
+ v (ρˡ (suc x)) ≡⟨⟩
+ tail (v ∘ ρˡ) x ∎
+ preimage- : [preimageρʳS]- ≗ preimage ρʳ- S-
+ preimage- x = begin
+ [preimageρʳS]- x ≡⟨⟩
+ removeAt (preimage ρʳ S) (head ρˡ) x ≡⟨⟩
+ S (ρʳ (punchIn (head ρˡ) x)) ≡⟨ ≡.cong S (punchIn-permute ρ (head ρˡ) x) ⟩ 
+ S (punchIn (ρʳ (head ρˡ)) (ρʳ- x)) ≡⟨⟩
+ S (punchIn (ρʳ (ρˡ zero)) (ρʳ- x)) ≡⟨ ≡.cong (λ h → S (punchIn h (ρʳ- x))) (inverseʳ ρ) ⟩ 
+ S (punchIn zero (ρʳ- x)) ≡⟨⟩ 
+ S (suc (ρʳ- x)) ≡⟨⟩
+ preimage ρʳ- S- x ∎
+
+push-with : {A B : ℕ} → (e : Value) → Vector Value A → (Fin A → Fin B) → Vector Value B
+push-with e v f = merge-with e v ∘ preimage f ∘ ⁅_⁆
+
+push : {A B : ℕ} → Vector Value A → (Fin A → Fin B) → Vector Value B
+push = push-with U
+
+mutual
+ merge-preimage
+ : {A B : ℕ}
+ (f : Fin A → Fin B)
+ → (v : Vector Value A)
+ (S : Subset B)
+ → merge v (preimage f S) ≡ merge (push v f) S
+ merge-preimage {zero} {zero} f v S = merge-[]₂
+ merge-preimage {zero} {suc B} f v S = begin
+ merge v (preimage f S) ≡⟨ merge-[] v (preimage f S) ⟩
+ U ≡⟨ merge-with-U U S ⟨
+ merge (λ _ → U) S ≡⟨ merge-cong₁ (λ x → ≡.sym (merge-[] v (⁅ x ⁆ ∘ f))) S ⟩
+ merge (push v f) S ∎
+ where
+ open ≡.≡-Reasoning
+ merge-preimage {suc A} {zero} f v S with () ← f zero
+ merge-preimage {suc A} {suc B} f v S with insert-f0-0 f
+ ... | ρ , ρf0≡0 = begin
+ merge v (preimage f S) ≡⟨ merge-cong₂ v (preimage-cong₁ (λ x → inverseˡ ρ {f x}) S) ⟨
+ merge v (preimage (ρˡ ∘ ρʳ ∘ f) S) ≡⟨⟩
+ merge v (preimage (ρʳ ∘ f) (preimage ρˡ S)) ≡⟨ merge-preimage-f0≡0 (ρʳ ∘ f) ρf0≡0 v (preimage ρˡ S) ⟩
+ merge (merge v ∘ preimage (ρʳ ∘ f) ∘ ⁅_⁆) (preimage ρˡ S) ≡⟨ merge-preimage-ρ (flip ρ) (merge v ∘ preimage (ρʳ ∘ f) ∘ ⁅_⁆) S ⟩
+ merge (merge v ∘ preimage (ρʳ ∘ f) ∘ ⁅_⁆ ∘ ρʳ) S ≡⟨ merge-cong₁ (merge-cong₂ v ∘ preimage-cong₂ (ρʳ ∘ f) ∘ ⁅⁆∘ρ ρ) S ⟩
+ merge (merge v ∘ preimage (ρʳ ∘ f) ∘ preimage ρˡ ∘ ⁅_⁆) S ≡⟨⟩
+ merge (merge v ∘ preimage (ρˡ ∘ ρʳ ∘ f) ∘ ⁅_⁆) S ≡⟨ merge-cong₁ (merge-cong₂ v ∘ preimage-cong₁ (λ y → inverseˡ ρ {f y}) ∘ ⁅_⁆) S ⟩
+ merge (merge v ∘ preimage f ∘ ⁅_⁆) S ∎
+ where
+ open ≡.≡-Reasoning
+ ρʳ ρˡ : Fin (ℕ.suc B) → Fin (ℕ.suc B)
+ ρʳ = ρ ⟨$⟩ʳ_
+ ρˡ = ρ ⟨$⟩ˡ_
+
+ merge-preimage-f0≡0
+ : {A B : ℕ}
+ (f : Fin (ℕ.suc A) → Fin (ℕ.suc B))
+ → f Fin.zero ≡ Fin.zero
+ → (v : Vector Value (ℕ.suc A))
+ (S : Subset (ℕ.suc B))
+ → merge v (preimage f S) ≡ merge (merge v ∘ preimage f ∘ ⁅_⁆) S
+ merge-preimage-f0≡0 {A} {B} f f0≡0 v S
+ using S0 , S- ← head S , tail S
+ using v0 , v- ← head v , tail v
+ using _ , f- ← head f , tail f
+ = begin
+ merge v f⁻¹[S] ≡⟨ merge-suc v f⁻¹[S] ⟩
+ merge-with v0? v- f⁻¹[S]- ≡⟨ join-merge v0? v- f⁻¹[S]- ⟨
+ join v0? (merge v- f⁻¹[S]-) ≡⟨ ≡.cong (join v0?) (merge-preimage f- v- S) ⟩
+ join v0? (merge f[v-] S) ≡⟨ join-merge v0? f[v-] S ⟩
+ merge-with v0? f[v-] S ≡⟨ merge-with-suc v0? f[v-] S ⟩
+ merge-with v0?+[f[v-]0?] f[v-]- S- ≡⟨ ≡.cong (λ h → merge-with h f[v-]- S-) ≡f[v]0 ⟩
+ merge-with f[v]0? f[v-]- S- ≡⟨ merge-with-cong f[v]0? ≡f[v]- S- ⟩
+ merge-with f[v]0? f[v]- S- ≡⟨ merge-suc f[v] S ⟨
+ merge f[v] S ∎
+ where
+ f⁻¹[S] : Subset (suc A)
+ f⁻¹[S] = preimage f S
+ f⁻¹[S]- : Subset A
+ f⁻¹[S]- = tail f⁻¹[S]
+ f⁻¹[S]0 : Bool
+ f⁻¹[S]0 = head f⁻¹[S]
+ f[v] : Vector Value (suc B)
+ f[v] = push v f
+ f[v]- : Vector Value B
+ f[v]- = tail f[v]
+ f[v]0 : Value
+ f[v]0 = head f[v]
+ f[v-] : Vector Value (suc B)
+ f[v-] = push v- f-
+ f[v-]- : Vector Value B
+ f[v-]- = tail f[v-]
+ f[v-]0 : Value
+ f[v-]0 = head f[v-]
+ f⁻¹⁅0⁆ : Subset (suc A)
+ f⁻¹⁅0⁆ = preimage f ⁅ zero ⁆
+ f⁻¹⁅0⁆- : Subset A
+ f⁻¹⁅0⁆- = tail f⁻¹⁅0⁆
+ v0? v0?+[f[v-]0?] f[v]0? : Value
+ v0? = v0 when f⁻¹[S]0
+ v0?+[f[v-]0?] = (if S0 then join v0? f[v-]0 else v0?)
+ f[v]0? = f[v]0 when S0
+ open ≡.≡-Reasoning
+ ≡f[v]0 : v0?+[f[v-]0?] ≡ f[v]0?
+ ≡f[v]0 rewrite f0≡0 with S0
+ ... | true = begin
+ join v0 (merge v- f⁻¹⁅0⁆-) ≡⟨ join-merge v0 v- (tail (preimage f ⁅ zero ⁆)) ⟩
+ merge-with v0 v- f⁻¹⁅0⁆- ≡⟨ ≡.cong (λ h → merge-with (v0 when ⁅ zero ⁆ h) v- f⁻¹⁅0⁆-) f0≡0 ⟨
+ merge-with v0?′ v- f⁻¹⁅0⁆- ≡⟨ merge-suc v (preimage f ⁅ zero ⁆) ⟨
+ merge v f⁻¹⁅0⁆  ∎
+ where
+ v0?′ : Value
+ v0?′ = v0 when head f⁻¹⁅0⁆
+ ... | false = ≡.refl
+ ≡f[v]- : f[v-]- ≗ f[v]-
+ ≡f[v]- x = begin
+ push v- f- (suc x) ≡⟨ ≡.cong (λ h → merge-with (v0 when ⁅ suc x ⁆ h) v- (preimage f- ⁅ suc x ⁆)) f0≡0 ⟨
+ push-with v0?′ v- f- (suc x) ≡⟨ merge-suc v (preimage f ⁅ suc x ⁆) ⟨
+ push v f (suc x) ∎
+ where
+ v0?′ : Value
+ v0?′ = v0 when head (preimage f ⁅ suc x ⁆)
diff --git a/Data/Circuit/Value.agda b/Data/Circuit/Value.agda
new file mode 100644
index 0000000..512a622
--- /dev/null
+++ b/Data/Circuit/Value.agda
@@ -0,0 +1,157 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Circuit.Value where
+
+open import Relation.Binary.Lattice.Bundles using (BoundedJoinSemilattice)
+open import Data.Product.Base using (_×_; _,_)
+open import Data.String.Base using (String)
+open import Level using (0ℓ)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_)
+
+data Value : Set where
+ U T F X : Value
+
+data ≤-Value : Value → Value → Set where
+ v≤v : {v : Value} → ≤-Value v v
+ U≤T : ≤-Value U T
+ U≤F : ≤-Value U F
+ U≤X : ≤-Value U X
+ T≤X : ≤-Value T X
+ F≤X : ≤-Value F X
+
+≤-reflexive : {x y : Value} → x ≡ y → ≤-Value x y
+≤-reflexive ≡.refl = v≤v
+
+≤-transitive : {i j k : Value} → ≤-Value i j → ≤-Value j k → ≤-Value i k
+≤-transitive v≤v y = y
+≤-transitive x v≤v = x
+≤-transitive U≤T T≤X = U≤X
+≤-transitive U≤F F≤X = U≤X
+
+≤-antisymmetric : {i j : Value} → ≤-Value i j → ≤-Value j i → i ≡ j
+≤-antisymmetric v≤v _ = ≡.refl
+
+showValue : Value → String
+showValue U = "U"
+showValue T = "T"
+showValue F = "F"
+showValue X = "X"
+
+join : Value → Value → Value
+join U y = y
+join x U = x
+join T T = T
+join T F = X
+join F T = X
+join F F = F
+join X _ = X
+join _ X = X
+
+≤-supremum
+ : (x y : Value)
+ → ≤-Value x (join x y)
+ × ≤-Value y (join x y)
+ × ((z : Value) → ≤-Value x z → ≤-Value y z → ≤-Value (join x y) z)
+≤-supremum U U = v≤v , v≤v , λ _ U≤z _ → U≤z
+≤-supremum U T = U≤T , v≤v , λ { z x≤z y≤z → y≤z }
+≤-supremum U F = U≤F , v≤v , λ { z x≤z y≤z → y≤z }
+≤-supremum U X = U≤X , v≤v , λ { z x≤z y≤z → y≤z }
+≤-supremum T U = v≤v , U≤T , λ { z x≤z y≤z → x≤z }
+≤-supremum T T = v≤v , v≤v , λ { z x≤z y≤z → x≤z }
+≤-supremum T F = T≤X , F≤X , λ { X x≤z y≤z → v≤v }
+≤-supremum T X = T≤X , v≤v , λ { z x≤z y≤z → y≤z }
+≤-supremum F U = v≤v , U≤F , λ { z x≤z y≤z → x≤z }
+≤-supremum F T = F≤X , T≤X , λ { X x≤z y≤z → v≤v }
+≤-supremum F F = v≤v , v≤v , λ { z x≤z y≤z → x≤z }
+≤-supremum F X = F≤X , v≤v , λ { z x≤z y≤z → y≤z }
+≤-supremum X U = v≤v , U≤X , λ { z x≤z y≤z → x≤z }
+≤-supremum X T = v≤v , T≤X , λ { z x≤z y≤z → x≤z }
+≤-supremum X F = v≤v , F≤X , λ { z x≤z y≤z → x≤z }
+≤-supremum X X = v≤v , v≤v , λ { z x≤z y≤z → x≤z }
+
+join-comm : (x y : Value) → join x y ≡ join y x
+join-comm U U = ≡.refl
+join-comm U T = ≡.refl
+join-comm U F = ≡.refl
+join-comm U X = ≡.refl
+join-comm T U = ≡.refl
+join-comm T T = ≡.refl
+join-comm T F = ≡.refl
+join-comm T X = ≡.refl
+join-comm F U = ≡.refl
+join-comm F T = ≡.refl
+join-comm F F = ≡.refl
+join-comm F X = ≡.refl
+join-comm X U = ≡.refl
+join-comm X T = ≡.refl
+join-comm X F = ≡.refl
+join-comm X X = ≡.refl
+
+join-assoc : (x y z : Value) → join (join x y) z ≡ join x (join y z)
+join-assoc U y z = ≡.refl
+join-assoc T U z = ≡.refl
+join-assoc T T U = ≡.refl
+join-assoc T T T = ≡.refl
+join-assoc T T F = ≡.refl
+join-assoc T T X = ≡.refl
+join-assoc T F U = ≡.refl
+join-assoc T F T = ≡.refl
+join-assoc T F F = ≡.refl
+join-assoc T F X = ≡.refl
+join-assoc T X U = ≡.refl
+join-assoc T X T = ≡.refl
+join-assoc T X F = ≡.refl
+join-assoc T X X = ≡.refl
+join-assoc F U z = ≡.refl
+join-assoc F T U = ≡.refl
+join-assoc F T T = ≡.refl
+join-assoc F T F = ≡.refl
+join-assoc F T X = ≡.refl
+join-assoc F F U = ≡.refl
+join-assoc F F T = ≡.refl
+join-assoc F F F = ≡.refl
+join-assoc F F X = ≡.refl
+join-assoc F X U = ≡.refl
+join-assoc F X T = ≡.refl
+join-assoc F X F = ≡.refl
+join-assoc F X X = ≡.refl
+join-assoc X U z = ≡.refl
+join-assoc X T U = ≡.refl
+join-assoc X T T = ≡.refl
+join-assoc X T F = ≡.refl
+join-assoc X T X = ≡.refl
+join-assoc X F U = ≡.refl
+join-assoc X F T = ≡.refl
+join-assoc X F F = ≡.refl
+join-assoc X F X = ≡.refl
+join-assoc X X U = ≡.refl
+join-assoc X X T = ≡.refl
+join-assoc X X F = ≡.refl
+join-assoc X X X = ≡.refl
+
+ValueLattice : BoundedJoinSemilattice 0ℓ 0ℓ 0ℓ
+ValueLattice = record
+ { Carrier = Value
+ ; _≈_ = _≡_
+ ; _≤_ = ≤-Value
+ ; _∨_ = join
+ ; ⊥ = U
+ ; isBoundedJoinSemilattice = record
+ { isJoinSemilattice = record
+ { isPartialOrder = record 
+ { isPreorder = record
+ { isEquivalence = ≡.isEquivalence
+ ; reflexive = ≤-reflexive
+ ; trans = ≤-transitive
+ }
+ ; antisym = ≤-antisymmetric
+ }
+ ; supremum = ≤-supremum
+ }
+ ; minimum = λ where
+ U → v≤v
+ T → U≤T
+ F → U≤F
+ X → U≤X
+ }
+ }
diff --git a/Data/Fin/Preimage.agda b/Data/Fin/Preimage.agda
new file mode 100644
index 0000000..4f7ea43
--- /dev/null
+++ b/Data/Fin/Preimage.agda
@@ -0,0 +1,48 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Fin.Preimage where
+
+open import Data.Nat.Base using (ℕ)
+open import Data.Fin.Base using (Fin)
+open import Function.Base using (∣_⟩-_; _∘_)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≗_)
+open import Data.Subset.Functional using (Subset; foldl; _∪_; ⊥; ⁅_⁆)
+
+private
+ variable A B C : ℕ
+
+preimage : (Fin A → Fin B) → Subset B → Subset A
+preimage f Y = Y ∘ f
+
+⋃ : Subset A → (Fin A → Subset B) → Subset B
+⋃ S f = foldl (∣ _∪_ ⟩- f) ⊥ S
+
+image : (Fin A → Fin B) → Subset A → Subset B
+image f X = ⋃ X (⁅_⁆ ∘ f)
+
+preimage-cong₁
+ : {f g : Fin A → Fin B}
+ → f ≗ g
+ → (S : Subset B)
+ → preimage f S ≗ preimage g S
+preimage-cong₁ f≗g S x = ≡.cong S (f≗g x)
+
+preimage-cong₂
+ : (f : Fin A → Fin B)
+ {S₁ S₂ : Subset B}
+ → S₁ ≗ S₂
+ → preimage f S₁ ≗ preimage f S₂
+preimage-cong₂ f S₁≗S₂ = S₁≗S₂ ∘ f
+
+preimage-∘
+ : (f : Fin A → Fin B)
+ (g : Fin B → Fin C)
+ (z : Fin C)
+ → preimage (g ∘ f) ⁅ z ⁆ ≗ preimage f (preimage g ⁅ z ⁆)
+preimage-∘ f g S x = ≡.refl
+
+preimage-⊥
+ : {n m : ℕ}
+ (f : Fin n → Fin m)
+ → preimage f ⊥ ≗ ⊥
+preimage-⊥ f x = ≡.refl
diff --git a/Data/Setoid.agda b/Data/Setoid.agda
new file mode 100644
index 0000000..454d276
--- /dev/null
+++ b/Data/Setoid.agda
@@ -0,0 +1,8 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Setoid where
+
+open import Relation.Binary using (Setoid)
+open import Function.Construct.Setoid using () renaming (setoid to infixr 0 _⇒ₛ_) public
+
+open Setoid renaming (Carrier to ∣_∣) public
diff --git a/Data/Subset/Functional.agda b/Data/Subset/Functional.agda
new file mode 100644
index 0000000..33a6d8e
--- /dev/null
+++ b/Data/Subset/Functional.agda
@@ -0,0 +1,162 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Subset.Functional where
+
+open import Data.Bool.Base using (Bool; _∨_; _∧_; if_then_else_)
+open import Data.Bool.Properties using (if-float)
+open import Data.Fin.Base using (Fin)
+open import Data.Fin.Permutation using (Permutation′; _⟨$⟩ʳ_; _⟨$⟩ˡ_; inverseˡ; inverseʳ)
+open import Data.Fin.Properties using (suc-injective; 0≢1+n)
+open import Data.Nat.Base using (ℕ)
+open import Function.Base using (∣_⟩-_; _∘_)
+open import Function.Definitions using (Injective)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≗_; _≢_)
+open import Data.Vector as V using (Vector; head; tail)
+
+open Bool
+open Fin
+open ℕ
+
+Subset : ℕ → Set
+Subset = Vector Bool
+
+private
+ variable n A : ℕ
+ variable B C : Set
+
+⊥ : Subset n
+⊥ _ = false
+
+_∪_ : Subset n → Subset n → Subset n
+(A ∪ B) k = A k ∨ B k
+
+_∩_ : Subset n → Subset n → Subset n
+(A ∩ B) k = A k ∧ B k
+
+⁅_⁆ : Fin n → Subset n
+⁅_⁆ zero zero = true
+⁅_⁆ zero (suc _) = false
+⁅_⁆ (suc k) zero = false
+⁅_⁆ (suc k) (suc i) = ⁅ k ⁆ i
+
+⁅⁆-refl : (k : Fin n) → ⁅ k ⁆ k ≡ true
+⁅⁆-refl zero = ≡.refl
+⁅⁆-refl (suc k) = ⁅⁆-refl k
+
+⁅x⁆y≡true
+ : (x y : Fin n)
+ → .(⁅ x ⁆ y ≡ true)
+ → x ≡ y
+⁅x⁆y≡true zero zero prf = ≡.refl
+⁅x⁆y≡true (suc x) (suc y) prf = ≡.cong suc (⁅x⁆y≡true x y prf)
+
+⁅x⁆y≡false
+ : (x y : Fin n)
+ → .(⁅ x ⁆ y ≡ false)
+ → x ≢ y
+⁅x⁆y≡false zero (suc y) prf = 0≢1+n
+⁅x⁆y≡false (suc x) zero prf = 0≢1+n ∘ ≡.sym
+⁅x⁆y≡false (suc x) (suc y) prf = ⁅x⁆y≡false x y prf ∘ suc-injective
+
+f-⁅⁆
+ : {n m : ℕ}
+ (f : Fin n → Fin m)
+ → Injective _≡_ _≡_ f
+ → (x y : Fin n)
+ → ⁅ x ⁆ y ≡ ⁅ f x ⁆ (f y)
+f-⁅⁆ f f-inj zero zero = ≡.sym (⁅⁆-refl (f zero))
+f-⁅⁆ f f-inj zero (suc y) with ⁅ f zero ⁆ (f (suc y)) in eq
+... | true with () ← f-inj (⁅x⁆y≡true (f zero) (f (suc y)) eq)
+... | false = ≡.refl
+f-⁅⁆ f f-inj (suc x) zero with ⁅ f (suc x) ⁆ (f zero) in eq
+... | true with () ← f-inj (⁅x⁆y≡true (f (suc x)) (f zero) eq)
+... | false = ≡.refl
+f-⁅⁆ f f-inj (suc x) (suc y) = f-⁅⁆ (f ∘ suc) (suc-injective ∘ f-inj) x y
+
+⁅⁆∘ρ
+ : (ρ : Permutation′ (suc n))
+ (x : Fin (suc n))
+ → ⁅ ρ ⟨$⟩ʳ x ⁆ ≗ ⁅ x ⁆ ∘ (ρ ⟨$⟩ˡ_)
+⁅⁆∘ρ {n} ρ x y = begin
+ ⁅ ρ ⟨$⟩ʳ x ⁆ y ≡⟨ f-⁅⁆ (ρ ⟨$⟩ˡ_) ρˡ-inj (ρ ⟨$⟩ʳ x) y ⟩
+ ⁅ ρ ⟨$⟩ˡ (ρ ⟨$⟩ʳ x) ⁆ (ρ ⟨$⟩ˡ y) ≡⟨ ≡.cong (λ h → ⁅ h ⁆ (ρ ⟨$⟩ˡ y)) (inverseˡ ρ) ⟩
+ ⁅ x ⁆ (ρ ⟨$⟩ˡ y) ∎
+ where
+ open ≡.≡-Reasoning
+ ρˡ-inj : {x y : Fin (suc n)} → ρ ⟨$⟩ˡ x ≡ ρ ⟨$⟩ˡ y → x ≡ y
+ ρˡ-inj {x} {y} ρˡx≡ρˡy = begin
+ x ≡⟨ inverseʳ ρ ⟨
+ ρ ⟨$⟩ʳ (ρ ⟨$⟩ˡ x) ≡⟨ ≡.cong (ρ ⟨$⟩ʳ_) ρˡx≡ρˡy ⟩
+ ρ ⟨$⟩ʳ (ρ ⟨$⟩ˡ y) ≡⟨ inverseʳ ρ ⟩
+ y ∎
+
+opaque
+ -- TODO dependent fold
+ foldl : (B → Fin A → B) → B → Subset A → B
+ foldl {B = B} f = V.foldl (λ _ → B) (λ { {k} acc b → if b then f acc k else acc })
+
+ foldl-cong₁
+ : {f g : B → Fin A → B}
+ → (∀ x y → f x y ≡ g x y)
+ → (e : B)
+ → (S : Subset A)
+ → foldl f e S ≡ foldl g e S
+ foldl-cong₁ {B = B} f≗g e S = V.foldl-cong (λ _ → B) (λ { {k} x y → ≡.cong (if y then_else x) (f≗g x k) }) e S
+
+ foldl-cong₂
+ : (f : B → Fin A → B)
+ (e : B)
+ {S₁ S₂ : Subset A}
+ → (S₁ ≗ S₂)
+ → foldl f e S₁ ≡ foldl f e S₂
+ foldl-cong₂ {B = B} f e S₁≗S₂ = V.foldl-cong-arg (λ _ → B) (λ {n} acc b → if b then f acc n else acc) e S₁≗S₂
+
+ foldl-suc
+ : (f : B → Fin (suc A) → B)
+ → (e : B)
+ → (S : Subset (suc A))
+ → foldl f e S ≡ foldl (∣ f ⟩- suc) (if head S then f e zero else e) (tail S)
+ foldl-suc f e S = ≡.refl
+
+ foldl-⊥
+ : {A : ℕ}
+ {B : Set}
+ (f : B → Fin A → B)
+ (e : B)
+ → foldl f e ⊥ ≡ e
+ foldl-⊥ {zero} _ _ = ≡.refl
+ foldl-⊥ {suc A} f e = foldl-⊥ (∣ f ⟩- suc) e
+
+ foldl-⁅⁆
+ : (f : B → Fin A → B)
+ (e : B)
+ (k : Fin A)
+ → foldl f e ⁅ k ⁆ ≡ f e k
+ foldl-⁅⁆ f e zero = foldl-⊥ f (f e zero)
+ foldl-⁅⁆ f e (suc k) = foldl-⁅⁆ (∣ f ⟩- suc) e k
+
+ foldl-fusion
+ : (h : C → B)
+ {f : C → Fin A → C}
+ {g : B → Fin A → B}
+ → (∀ x n → h (f x n) ≡ g (h x) n)
+ → (e : C)
+ → h ∘ foldl f e ≗ foldl g (h e)
+ foldl-fusion {C = C} {A = A} h {f} {g} fuse e = V.foldl-fusion h ≡.refl fuse′
+ where
+ open ≡.≡-Reasoning
+ fuse′
+ : {k : Fin A}
+ (acc : C)
+ (b : Bool)
+ → h (if b then f acc k else acc) ≡ (if b then g (h acc) k else h acc)
+ fuse′ {k} acc b = begin
+ h (if b then f acc k else acc) ≡⟨ if-float h b ⟩
+ (if b then h (f acc k) else h acc) ≡⟨ ≡.cong (if b then_else h acc) (fuse acc k) ⟩
+ (if b then g (h acc) k else h acc) ∎
+
+Subset0≗⊥ : (S : Subset 0) → S ≗ ⊥
+Subset0≗⊥ S ()
+
+foldl-[] : (f : B → Fin 0 → B) (e : B) (S : Subset 0) → foldl f e S ≡ e
+foldl-[] f e S = ≡.trans (foldl-cong₂ f e (Subset0≗⊥ S)) (foldl-⊥ f e)
diff --git a/Data/System.agda b/Data/System.agda
new file mode 100644
index 0000000..0361369
--- /dev/null
+++ b/Data/System.agda
@@ -0,0 +1,86 @@
+{-# OPTIONS --without-K --safe #-}
+
+open import Level using (Level)
+
+module Data.System {ℓ : Level} where
+
+import Function.Construct.Identity as Id
+import Relation.Binary.Properties.Preorder as PreorderProperties
+
+open import Data.Circuit.Value using (Value)
+open import Data.Nat.Base using (ℕ)
+open import Data.Setoid using (_⇒ₛ_; ∣_∣)
+open import Data.System.Values Value using (Values; _≋_; module ≋)
+open import Level using (Level; _⊔_; 0ℓ; suc)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_)
+open import Relation.Binary using (Reflexive; Transitive; Preorder; _⇒_; Setoid)
+open import Function.Base using (_∘_)
+open import Function.Bundles using (Func; _⟨$⟩_)
+open import Function.Construct.Setoid using (_∙_)
+
+open Func
+
+record System (n : ℕ) : Set (suc ℓ) where
+
+ field
+ S : Setoid ℓ ℓ
+ fₛ : ∣ Values n ⇒ₛ S ⇒ₛ S ∣
+ fₒ : ∣ S ⇒ₛ Values n ∣
+
+ fₛ′ : ∣ Values n ∣ → ∣ S ∣ → ∣ S ∣
+ fₛ′ = to ∘ to fₛ
+
+ fₒ′ : ∣ S ∣ → ∣ Values n ∣
+ fₒ′ = to fₒ
+
+ open Setoid S public
+
+module _ {n : ℕ} where
+
+ record ≤-System (a b : System n) : Set ℓ where
+ module A = System a
+ module B = System b
+ field
+ ⇒S : ∣ A.S ⇒ₛ B.S ∣
+ ≗-fₛ
+ : (i : ∣ Values n ∣) (s : ∣ A.S ∣)
+ → ⇒S ⟨$⟩ (A.fₛ′ i s) B.≈ B.fₛ′ i (⇒S ⟨$⟩ s)
+ ≗-fₒ
+ : (s : ∣ A.S ∣)
+ → A.fₒ′ s ≋ B.fₒ′ (⇒S ⟨$⟩ s)
+
+ open ≤-System
+
+ ≤-refl : Reflexive ≤-System
+ ⇒S ≤-refl = Id.function _
+ ≗-fₛ (≤-refl {x}) _ _ = System.refl x
+ ≗-fₒ (≤-refl {x}) _ = ≋.refl
+
+ ≡⇒≤ : _≡_ ⇒ ≤-System
+ ≡⇒≤ ≡.refl = ≤-refl
+
+ open System
+
+ ≤-trans : Transitive ≤-System
+ ⇒S (≤-trans a b) = ⇒S b ∙ ⇒S a
+ ≗-fₛ (≤-trans {x} {y} {z} a b) i s = System.trans z (cong (⇒S b) (≗-fₛ a i s)) (≗-fₛ b i (⇒S a ⟨$⟩ s))
+ ≗-fₒ (≤-trans a b) s = ≋.trans (≗-fₒ a s) (≗-fₒ b (⇒S a ⟨$⟩ s))
+
+ System-Preorder : Preorder (suc ℓ) (suc ℓ) ℓ
+ System-Preorder = record
+ { Carrier = System n
+ ; _≈_ = _≡_
+ ; _≲_ = ≤-System
+ ; isPreorder = record
+ { isEquivalence = ≡.isEquivalence
+ ; reflexive = ≡⇒≤
+ ; trans = ≤-trans
+ }
+ }
+
+module _ (n : ℕ) where
+
+ open PreorderProperties (System-Preorder {n}) using (InducedEquivalence)
+
+ Systemₛ : Setoid (suc ℓ) ℓ
+ Systemₛ = InducedEquivalence
diff --git a/Data/System/Values.agda b/Data/System/Values.agda
new file mode 100644
index 0000000..bf8fa38
--- /dev/null
+++ b/Data/System/Values.agda
@@ -0,0 +1,21 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.System.Values (A : Set) where
+
+open import Data.Nat.Base using (ℕ)
+open import Data.Vec.Functional using (Vector)
+open import Level using (0ℓ)
+open import Relation.Binary using (Rel; Setoid)
+open import Data.Vec.Functional.Relation.Binary.Equality.Setoid using (≋-setoid)
+
+import Relation.Binary.PropositionalEquality as ≡
+
+Values : ℕ → Setoid 0ℓ 0ℓ
+Values = ≋-setoid (≡.setoid A)
+
+_≋_ : {n : ℕ} → Rel (Vector A n) 0ℓ
+_≋_ {n} = Setoid._≈_ (Values n)
+
+infix 4 _≋_
+
+module ≋ {n : ℕ} = Setoid (Values n)
diff --git a/Data/Vector.agda b/Data/Vector.agda
new file mode 100644
index 0000000..052f624
--- /dev/null
+++ b/Data/Vector.agda
@@ -0,0 +1,82 @@
+{-# OPTIONS --without-K --safe #-}
+
+module Data.Vector where
+
+open import Data.Nat.Base using (ℕ)
+open import Data.Vec.Functional using (Vector; head; tail; []; removeAt; map) public
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≗_)
+open import Function.Base using (∣_⟩-_; _∘_)
+open import Data.Fin.Base using (Fin; toℕ)
+open ℕ
+open Fin
+
+foldl
+ : ∀ {n : ℕ} {A : Set} (B : ℕ → Set)
+ → (∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k)))
+ → B zero
+ → Vector A n
+ → B n
+foldl {zero} B ⊕ e v = e
+foldl {suc n} B ⊕ e v = foldl (B ∘ suc) ⊕ (⊕ e (head v)) (tail v)
+
+foldl-cong
+ : {n : ℕ} {A : Set}
+ (B : ℕ → Set)
+ {f g : ∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k))}
+ → (∀ {k} → ∀ x y → f {k} x y ≡ g {k} x y)
+ → (e : B zero)
+ → (v : Vector A n)
+ → foldl B f e v ≡ foldl B g e v
+foldl-cong {zero} B f≗g e v = ≡.refl
+foldl-cong {suc n} B {g = g} f≗g e v rewrite (f≗g e (head v)) = foldl-cong (B ∘ suc) f≗g (g e (head v)) (tail v)
+
+foldl-cong-arg
+ : {n : ℕ} {A : Set}
+ (B : ℕ → Set)
+ (f : ∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k)))
+ → (e : B zero)
+ → {v w : Vector A n}
+ → v ≗ w
+ → foldl B f e v ≡ foldl B f e w
+foldl-cong-arg {zero} B f e v≗w = ≡.refl
+foldl-cong-arg {suc n} B f e {w = w} v≗w rewrite v≗w zero = foldl-cong-arg (B ∘ suc) f (f e (head w)) (v≗w ∘ suc)
+
+foldl-map
+ : {n : ℕ} {A : ℕ → Set} {B C : Set}
+ (f : ∀ {k : Fin n} → A (toℕ k) → B → A (suc (toℕ k)))
+ (g : C → B)
+ (x : A zero)
+ (xs : Vector C n)
+ → foldl A f x (map g xs)
+ ≡ foldl A (∣ f ⟩- g) x xs
+foldl-map {zero} f g e xs = ≡.refl
+foldl-map {suc n} f g e xs = foldl-map f g (f e (g (head xs))) (tail xs)
+
+foldl-fusion
+ : {n : ℕ}
+ {A : Set} {B C : ℕ → Set}
+ (h : {k : ℕ} → B k → C k)
+ → {f : {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k))} {d : B zero}
+ → {g : {k : Fin n} → C (toℕ k) → A → C (suc (toℕ k))} {e : C zero}
+ → (h d ≡ e)
+ → ({k : Fin n} (b : B (toℕ k)) (x : A) → h (f {k} b x) ≡ g (h b) x)
+ → h ∘ foldl B f d ≗ foldl C g e
+foldl-fusion {zero} _ base _ _ = base
+foldl-fusion {suc n} {A} h {f} {d} {g} {e} base fuse xs = foldl-fusion h eq fuse (tail xs)
+ where
+ x₀ : A
+ x₀ = head xs
+ open ≡.≡-Reasoning
+ eq : h (f d x₀) ≡ g e x₀
+ eq = begin
+ h (f d x₀) ≡⟨ fuse d x₀ ⟩
+ g (h d) x₀ ≡⟨ ≡.cong-app (≡.cong g base) x₀ ⟩
+ g e x₀ ∎
+
+foldl-[]
+ : {A : Set}
+ (B : ℕ → Set)
+ (f : {k : Fin 0} → B (toℕ k) → A → B (suc (toℕ k)))
+ {e : B 0}
+ → foldl B f e [] ≡ e
+foldl-[] _ _ = ≡.refl