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diff --git a/Data/Circuit/Merge.agda b/Data/Circuit/Merge.agda new file mode 100644 index 0000000..9cf180a --- /dev/null +++ b/Data/Circuit/Merge.agda @@ -0,0 +1,427 @@ +{-# 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; splitAt) +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.Sum.Properties using ([,]-cong; [,-]-cong; [-,]-cong; [,]-∘; [,]-map) +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.Vec.Functional using (_++_) +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 (∣_⟩-_; _∘_; case_of_; _$_) +open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≢_; _≗_; module ≡-Reasoning) + +open Value using (U) +open ℕ +open Fin +open Bool + +open ≡-Reasoning + +_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 ∎ + +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 ⟨$⟩ʳ f zero ≡ zero + help with f zero ≟ f zero + ... | yes _ = ≡.refl + ... | no f0≢f0 with () ← f0≢f0 ≡.refl + +merge-removeAt + : {A : ℕ} + (k : Fin (suc A)) + (v : Vector Value (suc A)) + (S : Subset (suc A)) + → merge v S ≡ join (v k when S k) (merge (removeAt v k) (removeAt S k)) +merge-removeAt {A} zero v S = begin + merge-with U v S ≡⟨ merge-suc v S ⟩ + merge-with (head v when head S) (tail v) (tail S) ≡⟨ join-merge (head v when head S) (tail v) (tail S) ⟨ + join (head v when head S) (merge-with U (tail v) (tail S)) ∎ +merge-removeAt {suc A} (suc k) v S = begin + merge-with U v S ≡⟨ merge-suc v S ⟩ + merge-with v0? (tail v) (tail S) ≡⟨ join-merge _ (tail v) (tail S) ⟨ + join v0? (merge (tail v) (tail S)) ≡⟨ ≡.cong (join v0?) (merge-removeAt k (tail v) (tail S)) ⟩ + join v0? (join vk? (merge (tail v-) (tail S-))) ≡⟨ join-assoc (head v when head S) _ _ ⟨ + join (join v0? vk?) (merge (tail v-) (tail S-)) ≡⟨ ≡.cong (λ h → join h (merge (tail v-) (tail S-))) (join-comm (head v- when head S-) _) ⟩ + join (join vk? v0?) (merge (tail v-) (tail S-)) ≡⟨ join-assoc (tail v k when tail S k) _ _ ⟩ + join vk? (join v0? (merge (tail v-) (tail S-))) ≡⟨ ≡.cong (join vk?) (join-merge _ (tail v-) (tail S-)) ⟩ + join vk? (merge-with v0? (tail v-) (tail S-)) ≡⟨ ≡.cong (join vk?) (merge-suc v- S-) ⟨ + join vk? (merge v- S-) ∎ + where + v0? vk? : Value + v0? = head v when head S + vk? = tail v k when tail S k + v- : Vector Value (suc A) + v- = removeAt v (suc k) + S- : Subset (suc A) + S- = removeAt S (suc k) + +import Function.Structures as FunctionStructures +open module FStruct {A B : Set} = FunctionStructures {_} {_} {_} {_} {A} _≡_ {B} _≡_ using (IsInverse) +open IsInverse using () renaming (inverseˡ to invˡ; inverseʳ to invʳ) + +merge-preimage-ρ + : {A B : ℕ} + → (ρ : Permutation A B) + → (v : Vector Value A) + (S : Subset B) + → merge v (preimage (ρ ⟨$⟩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 + ≡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 ∎ + 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 + 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 + ≡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 ⁆) + +merge-++ + : {n m : ℕ} + (xs : Vector Value n) + (ys : Vector Value m) + (S₁ : Subset n) + (S₂ : Subset m) + → merge (xs ++ ys) (S₁ ++ S₂) + ≡ join (merge xs S₁) (merge ys S₂) +merge-++ {zero} {m} xs ys S₁ S₂ = begin + merge (xs ++ ys) (S₁ ++ S₂) ≡⟨ merge-cong₂ (xs ++ ys) (λ _ → ≡.refl) ⟩ + merge (xs ++ ys) S₂ ≡⟨ merge-cong₁ (λ _ → ≡.refl) S₂ ⟩ + merge ys S₂ ≡⟨ ≡.cong (λ h → join h (merge ys S₂)) (merge-[] xs S₁) ⟨ + join (merge xs S₁) (merge ys S₂) ∎ +merge-++ {suc n} {m} xs ys S₁ S₂ = begin + merge (xs ++ ys) (S₁ ++ S₂) ≡⟨ merge-suc (xs ++ ys) (S₁ ++ S₂) ⟩ + merge-with (head xs when head S₁) (tail (xs ++ ys)) (tail (S₁ ++ S₂)) ≡⟨ join-merge (head xs when head S₁) (tail (xs ++ ys)) (tail (S₁ ++ S₂)) ⟨ + join (head xs when head S₁) (merge (tail (xs ++ ys)) (tail (S₁ ++ S₂))) + ≡⟨ ≡.cong (join (head xs when head S₁)) (merge-cong₁ ([,]-map ∘ splitAt n) (tail (S₁ ++ S₂))) ⟩ + join (head xs when head S₁) (merge (tail xs ++ ys) (tail (S₁ ++ S₂))) + ≡⟨ ≡.cong (join (head xs when head S₁)) (merge-cong₂ (tail xs ++ ys) ([,]-map ∘ splitAt n)) ⟩ + join (head xs when head S₁) (merge (tail xs ++ ys) (tail S₁ ++ S₂)) ≡⟨ ≡.cong (join (head xs when head S₁)) (merge-++ (tail xs) ys (tail S₁) S₂) ⟩ + join (head xs when head S₁) (join (merge (tail xs) (tail S₁)) (merge ys S₂)) ≡⟨ join-assoc (head xs when head S₁) (merge (tail xs) (tail S₁)) _ ⟨ + join (join (head xs when head S₁) (merge (tail xs) (tail S₁))) (merge ys S₂) + ≡⟨ ≡.cong (λ h → join h (merge ys S₂)) (join-merge (head xs when head S₁) (tail xs) (tail S₁)) ⟩ + join (merge-with (head xs when head S₁) (tail xs) (tail S₁)) (merge ys S₂) ≡⟨ ≡.cong (λ h → join h (merge ys S₂)) (merge-suc xs S₁) ⟨ + join (merge xs S₁) (merge ys S₂) ∎ + +open import Function using (Equivalence) +open Equivalence +open import Data.Nat using (_+_) +open import Data.Fin using (_↑ˡ_; _↑ʳ_; _≟_) +open import Data.Fin.Properties using (↑ˡ-injective; ↑ʳ-injective; splitAt⁻¹-↑ˡ; splitAt-↑ˡ; splitAt⁻¹-↑ʳ; splitAt-↑ʳ) +open import Relation.Nullary.Decidable using (does; does-⇔; dec-false) + +open Fin +⁅⁆-≟ : {n : ℕ} (x y : Fin n) → ⁅ x ⁆ y ≡ does (x ≟ y) +⁅⁆-≟ zero zero = ≡.refl +⁅⁆-≟ zero (suc y) = ≡.refl +⁅⁆-≟ (suc x) zero = ≡.refl +⁅⁆-≟ (suc x) (suc y) = ⁅⁆-≟ x y + +open import Data.Sum using ([_,_]′; inj₁; inj₂) +⁅⁆-++ + : {n′ m′ : ℕ} + (i : Fin (n′ + m′)) + → [ (λ x → ⁅ x ⁆ ++ ⊥) , (λ x → ⊥ ++ ⁅ x ⁆) ]′ (splitAt n′ i) ≗ ⁅ i ⁆ +⁅⁆-++ {n′} {m′} i x with splitAt n′ i in eq₁ +... | inj₁ i′ with splitAt n′ x in eq₂ +... | inj₁ x′ = begin + ⁅ i′ ⁆ x′ ≡⟨ ⁅⁆-≟ i′ x′ ⟩ + does (i′ ≟ x′) ≡⟨ does-⇔ ⇔ (i′ ≟ x′) (i′ ↑ˡ m′ ≟ x′ ↑ˡ m′) ⟩ + does (i′ ↑ˡ m′ ≟ x′ ↑ˡ m′) ≡⟨ ⁅⁆-≟ (i′ ↑ˡ m′) (x′ ↑ˡ m′) ⟨ + ⁅ i′ ↑ˡ m′ ⁆ (x′ ↑ˡ m′) ≡⟨ ≡.cong₂ ⁅_⁆ (splitAt⁻¹-↑ˡ eq₁) (splitAt⁻¹-↑ˡ eq₂) ⟩ + ⁅ i ⁆ x ∎ + where + ⇔ : Equivalence (≡.setoid (i′ ≡ x′)) (≡.setoid (i′ ↑ˡ m′ ≡ x′ ↑ˡ m′)) + ⇔ .to = ≡.cong (_↑ˡ m′) + ⇔ .from = ↑ˡ-injective m′ i′ x′ + ⇔ .to-cong ≡.refl = ≡.refl + ⇔ .from-cong ≡.refl = ≡.refl +... | inj₂ x′ = begin + false ≡⟨ dec-false (i′ ↑ˡ m′ ≟ n′ ↑ʳ x′) ↑ˡ≢↑ʳ ⟨ + does (i′ ↑ˡ m′ ≟ n′ ↑ʳ x′) ≡⟨ ⁅⁆-≟ (i′ ↑ˡ m′) (n′ ↑ʳ x′) ⟨ + ⁅ i′ ↑ˡ m′ ⁆ (n′ ↑ʳ x′) ≡⟨ ≡.cong₂ ⁅_⁆ (splitAt⁻¹-↑ˡ eq₁) (splitAt⁻¹-↑ʳ eq₂) ⟩ + ⁅ i ⁆ x ∎ + where + ↑ˡ≢↑ʳ : i′ ↑ˡ m′ ≢ n′ ↑ʳ x′ + ↑ˡ≢↑ʳ ≡ = case ≡.trans (≡.sym (splitAt-↑ˡ n′ i′ m′)) (≡.trans (≡.cong (splitAt n′) ≡) (splitAt-↑ʳ n′ m′ x′)) of λ { () } +⁅⁆-++ {n′} i x | inj₂ i′ with splitAt n′ x in eq₂ +⁅⁆-++ {n′} {m′} i x | inj₂ i′ | inj₁ x′ = begin + [ ⊥ , ⁅ i′ ⁆ ]′ (splitAt n′ x) ≡⟨ ≡.cong ([ ⊥ , ⁅ i′ ⁆ ]′) eq₂ ⟩ + false ≡⟨ dec-false (n′ ↑ʳ i′ ≟ x′ ↑ˡ m′) ↑ʳ≢↑ˡ ⟨ + does (n′ ↑ʳ i′ ≟ x′ ↑ˡ m′) ≡⟨ ⁅⁆-≟ (n′ ↑ʳ i′) (x′ ↑ˡ m′) ⟨ + ⁅ n′ ↑ʳ i′ ⁆ (x′ ↑ˡ m′) ≡⟨ ≡.cong₂ ⁅_⁆ (splitAt⁻¹-↑ʳ eq₁) (splitAt⁻¹-↑ˡ eq₂) ⟩ + ⁅ i ⁆ x ∎ + where + ↑ʳ≢↑ˡ : n′ ↑ʳ i′ ≢ x′ ↑ˡ m′ + ↑ʳ≢↑ˡ ≡ = case ≡.trans (≡.sym (splitAt-↑ʳ n′ m′ i′)) (≡.trans (≡.cong (splitAt n′) ≡) (splitAt-↑ˡ n′ x′ m′)) of λ { () } +⁅⁆-++ {n′} i x | inj₂ i′ | inj₂ x′ = begin + [ ⊥ , ⁅ i′ ⁆ ]′ (splitAt n′ x) ≡⟨ ≡.cong [ ⊥ , ⁅ i′ ⁆ ]′ eq₂ ⟩ + ⁅ i′ ⁆ x′ ≡⟨ ⁅⁆-≟ i′ x′ ⟩ + does (i′ ≟ x′) ≡⟨ does-⇔ ⇔ (i′ ≟ x′) (n′ ↑ʳ i′ ≟ n′ ↑ʳ x′) ⟩ + does (n′ ↑ʳ i′ ≟ n′ ↑ʳ x′) ≡⟨ ⁅⁆-≟ (n′ ↑ʳ i′) (n′ ↑ʳ x′) ⟨ + ⁅ n′ ↑ʳ i′ ⁆ (n′ ↑ʳ x′) ≡⟨ ≡.cong₂ ⁅_⁆ (splitAt⁻¹-↑ʳ eq₁) (splitAt⁻¹-↑ʳ eq₂) ⟩ + ⁅ i ⁆ x ∎ + where + ⇔ : Equivalence (≡.setoid (i′ ≡ x′)) (≡.setoid (n′ ↑ʳ i′ ≡ n′ ↑ʳ x′)) + ⇔ .to = ≡.cong (n′ ↑ʳ_) + ⇔ .from = ↑ʳ-injective n′ i′ x′ + ⇔ .to-cong ≡.refl = ≡.refl + ⇔ .from-cong ≡.refl = ≡.refl |