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+{-# OPTIONS --without-K --safe #-}
+
+module Functor.Monoidal.Instance.Nat.Push where
+
+open import Categories.Category.Instance.Nat using (Nat)
+open import Data.Bool.Base using (Bool; false)
+open import Data.Subset.Functional using (Subset; ⁅_⁆; ⊥)
+open import Function.Base using (_∘_; case_of_; _$_; id)
+open import Function.Bundles using (Func; _⟶ₛ_; _⟨$⟩_)
+open import Level using (0ℓ; Level)
+open import Relation.Binary using (Rel; Setoid)
+open import Functor.Instance.Nat.Push using (Push; Push₁; Push-identity)
+open import Categories.Category.Instance.SingletonSet using (SingletonSetoid)
+open import Categories.NaturalTransformation using (NaturalTransformation; ntHelper)
+open import Data.Vec.Functional using (Vector; []; _++_; head; tail)
+open import Data.Vec.Functional.Properties using (++-cong)
+open import Categories.Category.Monoidal.Instance.Setoids using (Setoids-Cartesian)
+open import Categories.Category.BinaryProducts using (module BinaryProducts)
+open import Categories.Category.Cartesian using (Cartesian)
+open Cartesian (Setoids-Cartesian {0ℓ} {0ℓ}) using (products)
+open import Category.Cocomplete.Finitely.Bundle using (FinitelyCocompleteCategory)
+open import Categories.Category.Instance.Nat using (Nat-Cocartesian)
+open import Categories.Category.Cocartesian using (Cocartesian; module BinaryCoproducts)
+open import Categories.Category.Product using (_⁂_)
+open import Categories.Functor using () renaming (_∘F_ to _∘′_)
+open Cocartesian Nat-Cocartesian using (module Dual; i₁; i₂; -+-; _+₁_; +-assoc; +-assocʳ; +-assocˡ; +-comm; +-swap; +₁∘+-swap)
+open import Data.Product.Relation.Binary.Pointwise.NonDependent using (_×ₛ_)
+open import Data.Nat.Base using (ℕ; _+_)
+open import Data.Fin.Base using (Fin)
+open import Data.Product.Base using (_,_; _×_; Σ)
+open import Data.Fin.Preimage using (preimage; preimage-⊥; preimage-cong₂)
+open import Functor.Monoidal.Instance.Nat.Preimage using (preimage-++)
+open import Data.Sum.Base using ([_,_]; [_,_]′; inj₁; inj₂)
+open import Data.Sum.Properties using ([,]-cong; [,-]-cong; [-,]-cong; [,]-∘; [,]-map)
+open import Data.Circuit.Merge using (merge-with; merge; merge-⊥; merge-[]; merge-cong₁; merge-cong₂; merge-suc; _when_; join-merge; merge-preimage-ρ; merge-⁅⁆)
+open import Data.Circuit.Value using (Value; join; join-comm; join-assoc)
+open import Data.Fin.Base using (splitAt; _↑ˡ_; _↑ʳ_) renaming (join to joinAt)
+open import Data.Fin.Properties using (splitAt-↑ˡ; splitAt-↑ʳ; splitAt⁻¹-↑ˡ; splitAt⁻¹-↑ʳ; ↑ˡ-injective; ↑ʳ-injective; _≟_; 2↔Bool)
+open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≢_; _≗_; module ≡-Reasoning)
+open BinaryProducts products using (-×-)
+open Value using (U)
+open Bool using (false)
+
+open import Function.Bundles using (Equivalence)
+open import Category.Monoidal.Instance.Nat using (Nat,+,0)
+open import Category.Instance.Setoids.SymmetricMonoidal {0ℓ} {0ℓ} using (Setoids-×)
+open import Categories.Functor.Monoidal.Symmetric Nat,+,0 Setoids-× using (module Lax)
+open Lax using (SymmetricMonoidalFunctor)
+open import Categories.Morphism Nat using (_≅_)
+open import Function.Bundles using (Inverse)
+open import Data.Fin.Permutation using (Permutation; _⟨$⟩ʳ_; _⟨$⟩ˡ_)
+open Dual.op-binaryProducts using () renaming (assocˡ∘⟨⟩ to []∘assocʳ; swap∘⟨⟩ to []∘swap)
+open import Relation.Nullary.Decidable using (does; does-⇔; dec-false)
+
+open import Data.System.Values Value using (Values)
+
+open Func
+Push-ε : SingletonSetoid {0ℓ} {0ℓ} ⟶ₛ Values 0
+to Push-ε x = []
+cong Push-ε x ()
+
+++ₛ : {n m : ℕ} → Values n ×ₛ Values m ⟶ₛ Values (n + m)
+to ++ₛ (xs , ys) = xs ++ ys
+cong ++ₛ (≗xs , ≗ys) = ++-cong _ _ ≗xs ≗ys
+
+∣_∣ : {c ℓ : Level} → Setoid c ℓ → Set c
+∣_∣ = Setoid.Carrier
+
+open ℕ
+merge-++
+    : {n m : ℕ}
+      (xs : ∣ Values n ∣)
+      (ys : ∣ Values 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)  ∎
+  where
+    open ≡-Reasoning
+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)                                              ∎
+  where
+    open ≡-Reasoning
+
+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
+
+Push-++
+    : {n n′ m m′ : ℕ}
+      (f : Fin n → Fin n′)
+      (g : Fin m → Fin m′)
+      (xs : ∣ Values n ∣)
+      (ys : ∣ Values m ∣)
+    → merge xs ∘ preimage f ∘ ⁅_⁆ ++ merge ys ∘ preimage g ∘ ⁅_⁆
+    ≗ merge (xs ++ ys) ∘ preimage (f +₁ g) ∘ ⁅_⁆
+Push-++ {n} {n′} {m} {m′} f g xs ys i = begin
+    ((merge xs ∘ preimage f ∘ ⁅_⁆) ++ (merge ys ∘ preimage g ∘ ⁅_⁆)) i ≡⟨⟩
+    [ merge xs ∘ preimage f ∘ ⁅_⁆ , merge ys ∘ preimage g ∘ ⁅_⁆ ]′ (splitAt n′ i)
+        ≡⟨ [,]-cong left right (splitAt n′ i) ⟩
+    [ (λ x → merge (xs ++ ys) _) , (λ x → merge (xs ++ ys) _) ]′ (splitAt n′ i)
+        ≡⟨ [,]-∘ (merge (xs ++ ys) ∘ (preimage (f +₁ g))) (splitAt n′ i) ⟨
+    merge (xs ++ ys) (preimage (f +₁ g) ([ ⁅⁆++⊥ , ⊥++⁅⁆ ]′ (splitAt n′ i))) ≡⟨⟩
+    merge (xs ++ ys) (preimage (f +₁ g) ((⁅⁆++⊥ ++ ⊥++⁅⁆) i)) ≡⟨ merge-cong₂ (xs ++ ys) (preimage-cong₂ (f +₁ g) (⁅⁆-++ i)) ⟩
+    merge (xs ++ ys) (preimage (f +₁ g) ⁅ i ⁆) ∎
+  where
+    open ≡-Reasoning
+    left : (x : Fin n′) → merge xs (preimage f ⁅ x ⁆) ≡ merge (xs ++ ys) (preimage (f +₁ g) (⁅ x ⁆ ++ ⊥))
+    left x = begin
+        merge xs (preimage f ⁅ x ⁆)                                   ≡⟨ join-comm U (merge xs (preimage f ⁅ x ⁆)) ⟩
+        join (merge xs (preimage f ⁅ x ⁆)) U                          ≡⟨ ≡.cong (join (merge _ _)) (merge-⊥ ys) ⟨
+        join (merge xs (preimage f ⁅ x ⁆)) (merge ys ⊥)               ≡⟨ ≡.cong (join (merge _ _)) (merge-cong₂ ys (preimage-⊥ g)) ⟨
+        join (merge xs (preimage f ⁅ x ⁆)) (merge ys (preimage g ⊥))  ≡⟨ merge-++ xs ys (preimage f ⁅ x ⁆) (preimage g ⊥) ⟨
+        merge (xs ++ ys) ((preimage f ⁅ x ⁆) ++ (preimage g ⊥))       ≡⟨ merge-cong₂ (xs ++ ys) (preimage-++ f g) ⟩
+        merge (xs ++ ys) (preimage (f +₁ g) (⁅ x ⁆ ++ ⊥))             ∎
+    right : (x : Fin m′) → merge ys (preimage g ⁅ x ⁆) ≡ merge (xs ++ ys) (preimage (f +₁ g) (⊥ ++ ⁅ x ⁆))
+    right x = begin
+        merge ys (preimage g ⁅ x ⁆)                                   ≡⟨⟩
+        join U (merge ys (preimage g ⁅ x ⁆))                          ≡⟨ ≡.cong (λ h → join h (merge _ _)) (merge-⊥ xs) ⟨
+        join (merge xs ⊥) (merge ys (preimage g ⁅ x ⁆))               ≡⟨ ≡.cong (λ h → join h (merge _ _)) (merge-cong₂ xs (preimage-⊥ f)) ⟨
+        join (merge xs (preimage f ⊥)) (merge ys (preimage g ⁅ x ⁆))  ≡⟨ merge-++ xs ys (preimage f ⊥) (preimage g ⁅ x ⁆) ⟨
+        merge (xs ++ ys) ((preimage f ⊥) ++ (preimage g ⁅ x ⁆))       ≡⟨ merge-cong₂ (xs ++ ys) (preimage-++ f g) ⟩
+        merge (xs ++ ys) (preimage (f +₁ g) (⊥ ++ ⁅ x ⁆))             ∎
+    ⁅⁆++⊥ : Vector (Subset (n′ + m′)) n′
+    ⁅⁆++⊥ x = ⁅ x ⁆ ++ ⊥
+    ⊥++⁅⁆ : Vector (Subset (n′ + m′)) m′
+    ⊥++⁅⁆ x = ⊥ ++ ⁅ x ⁆
+
+    open ℕ
+
+    open Equivalence
+
+    ⁅⁆-++
+        : (i : Fin (n′ + m′))
+        → [ (λ x → ⁅ x ⁆ ++ ⊥) , (λ x → ⊥ ++ ⁅ x ⁆) ]′ (splitAt n′ i) ≗ ⁅ i ⁆
+    ⁅⁆-++ 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 { () }
+    ⁅⁆-++ i x | inj₂ i′ with splitAt n′ x in eq₂
+    ⁅⁆-++ i x | inj₂ i′ | inj₁ x′ = ≡.trans (≡.cong ([ ⊥ , ⁅ i′ ⁆ ]′) eq₂) $ begin
+        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 { () }
+    ⁅⁆-++ 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
+
+⊗-homomorphism : NaturalTransformation (-×- ∘′ (Push ⁂ Push)) (Push ∘′ -+-)
+⊗-homomorphism = ntHelper record
+    { η = λ (n , m) → ++ₛ {n} {m}
+    ; commute = λ { {n , m} {n′ , m′} (f , g) {xs , ys} i → Push-++ f g xs ys i }
+    }
+
+++-↑ˡ
+    : {n m : ℕ}
+      (X : ∣ Values n ∣)
+      (Y : ∣ Values m ∣)
+    → (X ++ Y) ∘ i₁ ≗ X
+++-↑ˡ {n} {m} X Y i = ≡.cong [ X , Y ]′ (splitAt-↑ˡ n i m)
+
+++-↑ʳ
+    : {n m : ℕ}
+      (X : ∣ Values n ∣)
+      (Y : ∣ Values m ∣)
+    → (X ++ Y) ∘ i₂ ≗ Y
+++-↑ʳ {n} {m} X Y i = ≡.cong [ X , Y ]′ (splitAt-↑ʳ n m i)
+
+++-assoc
+    : {m n o : ℕ}
+      (X : ∣ Values m ∣)
+      (Y : ∣ Values n ∣)
+      (Z : ∣ Values o ∣)
+    → ((X ++ Y) ++ Z) ∘ +-assocʳ {m} ≗ X ++ (Y ++ Z)
+++-assoc {m} {n} {o} X Y Z i = begin
+    ((X ++ Y) ++ Z) (+-assocʳ {m} i)                                    ≡⟨⟩
+    ((X ++ Y) ++ Z) ([ i₁ ∘ i₁ , _ ]′ (splitAt m i))                    ≡⟨ [,]-∘ ((X ++ Y) ++ Z) (splitAt m i) ⟩
+    [ ((X ++ Y) ++ Z) ∘ i₁ ∘ i₁ , _ ]′ (splitAt m i)                    ≡⟨ [-,]-cong (++-↑ˡ (X ++ Y) Z ∘ i₁) (splitAt m i) ⟩
+    [ (X ++ Y) ∘ i₁ , _ ]′ (splitAt m i)                                ≡⟨ [-,]-cong (++-↑ˡ X Y) (splitAt m i) ⟩
+    [ X , ((X ++ Y) ++ Z) ∘ [ _ , _ ]′ ∘ splitAt n ]′ (splitAt m i)     ≡⟨ [,-]-cong ([,]-∘ ((X ++ Y) ++ Z) ∘ splitAt n) (splitAt m i) ⟩
+    [ X , [ (_ ++ Z) ∘ i₁ ∘ i₂ {m} , _ ]′ ∘ splitAt n ]′ (splitAt m i)  ≡⟨ [,-]-cong ([-,]-cong (++-↑ˡ (X ++ Y) Z ∘ i₂) ∘ splitAt n) (splitAt m i) ⟩
+    [ X , [ (X ++ Y) ∘ i₂ , _ ]′ ∘ splitAt n ]′ (splitAt m i)           ≡⟨ [,-]-cong ([-,]-cong (++-↑ʳ X Y) ∘ splitAt n) (splitAt m i) ⟩
+    [ X , [ Y , ((X ++ Y) ++ Z) ∘ i₂ ]′ ∘ splitAt n ]′ (splitAt m i)    ≡⟨ [,-]-cong ([,-]-cong (++-↑ʳ (X ++ Y) Z) ∘ splitAt n) (splitAt m i) ⟩
+    [ X , [ Y , Z ]′ ∘ splitAt n ]′ (splitAt m i)                       ≡⟨⟩
+    (X ++ (Y ++ Z)) i                                                   ∎
+  where
+    open Bool
+    open Fin
+    open ≡-Reasoning
+
+Preimage-unitaryˡ
+    : {n : ℕ}
+      (X : Subset n)
+    → (X ++ []) ∘ (_↑ˡ 0) ≗ X
+Preimage-unitaryˡ {n} X i = begin
+    [ X , [] ]′ (splitAt _ (i ↑ˡ 0))  ≡⟨ ≡.cong ([ X , [] ]′) (splitAt-↑ˡ n i 0) ⟩
+    [ X , [] ]′ (inj₁ i)              ≡⟨⟩
+    X i                               ∎
+  where
+    open ≡-Reasoning
+
+Push-assoc
+    : {m n o : ℕ}
+      (X : ∣ Values m ∣)
+      (Y : ∣ Values n ∣)
+      (Z : ∣ Values o ∣)
+    → merge ((X ++ Y) ++ Z) ∘ preimage (+-assocˡ {m}) ∘  ⁅_⁆
+    ≗ X ++ (Y ++ Z)
+Push-assoc {m} {n} {o} X Y Z i = begin
+    merge ((X ++ Y) ++ Z) (preimage (+-assocˡ {m}) ⁅ i ⁆)         ≡⟨ merge-preimage-ρ ↔-mno ((X ++ Y) ++ Z) ⁅ i ⁆ ⟩
+    merge (((X ++ Y) ++ Z) ∘ (+-assocʳ {m})) (⁅ i ⁆)              ≡⟨⟩
+    merge (((X ++ Y) ++ Z) ∘ (+-assocʳ {m})) (preimage id ⁅ i ⁆)  ≡⟨ merge-cong₁ (++-assoc X Y Z) (preimage id ⁅ i ⁆) ⟩
+    merge (X ++ (Y ++ Z)) (preimage id ⁅ i ⁆)                     ≡⟨ Push-identity i ⟩
+    (X ++ (Y ++ Z)) i                                             ∎
+  where
+    open Inverse
+    module +-assoc = _≅_ (+-assoc {m} {n} {o})
+    ↔-mno : Permutation ((m + n) + o) (m + (n + o))
+    ↔-mno .to = +-assocˡ {m}
+    ↔-mno .from = +-assocʳ {m}
+    ↔-mno .to-cong ≡.refl = ≡.refl
+    ↔-mno .from-cong ≡.refl = ≡.refl
+    ↔-mno .inverse = (λ { ≡.refl → +-assoc.isoˡ _ }) , λ { ≡.refl → +-assoc.isoʳ _ }
+    open ≡-Reasoning
+
+preimage-++′
+    : {n m o : ℕ}
+      (f : Vector (Fin o) n)
+      (g : Vector (Fin o) m)
+      (S : Subset o)
+    → preimage (f ++ g) S ≗ preimage f S ++ preimage g S
+preimage-++′ {n} f g S = [,]-∘ S ∘ splitAt n
+
+Push-unitaryʳ
+    : {n : ℕ}
+      (X : ∣ Values n ∣)
+      (i : Fin n)
+    → merge (X ++ []) (preimage (id ++ (λ ())) ⁅ i ⁆) ≡ X i
+Push-unitaryʳ {n} X i = begin
+    merge (X ++ []) (preimage (id ++ (λ ())) ⁅ i ⁆)               ≡⟨ merge-cong₂ (X ++ []) (preimage-++′ id (λ ()) ⁅ i ⁆) ⟩
+    merge (X ++ []) (preimage id ⁅ i ⁆ ++ preimage (λ ()) ⁅ i ⁆)  ≡⟨⟩
+    merge (X ++ []) (⁅ i ⁆ ++ preimage (λ ()) ⁅ i ⁆)              ≡⟨ merge-++ X [] ⁅ i ⁆ (preimage (λ ()) ⁅ i ⁆) ⟩
+    join (merge X ⁅ i ⁆) (merge [] (preimage (λ ()) ⁅ i ⁆))       ≡⟨ ≡.cong (join (merge X ⁅ i ⁆)) (merge-[] [] (preimage (λ ()) ⁅ i ⁆)) ⟩
+    join (merge X ⁅ i ⁆) U                                        ≡⟨ join-comm (merge X ⁅ i ⁆) U ⟩
+    merge X ⁅ i ⁆                                                 ≡⟨ merge-⁅⁆ X i ⟩
+    X i ∎
+  where
+    open ≡-Reasoning
+    t : Fin (n + 0) → Fin n
+    t = id ++ (λ ())
+
+Push-swap
+    : {n m : ℕ}
+      (X : ∣ Values n ∣)
+      (Y : ∣ Values m ∣)
+    → merge (X ++ Y) ∘ preimage (+-swap {m}) ∘ ⁅_⁆ ≗ Y ++ X
+Push-swap {n} {m} X Y i = begin
+    merge (X ++ Y) (preimage (+-swap {m}) ⁅ i ⁆)      ≡⟨ merge-preimage-ρ n+m↔m+n (X ++ Y) ⁅ i ⁆ ⟩
+    merge ((X ++ Y) ∘ +-swap {n}) ⁅ i ⁆               ≡⟨ merge-⁅⁆ ((X ++ Y) ∘ (+-swap {n})) i ⟩
+    ((X ++ Y) ∘ +-swap {n}) i                         ≡⟨ [,]-∘ (X ++ Y) (splitAt m i) ⟩
+    [ (X ++ Y) ∘ i₂ , (X ++ Y) ∘ i₁ ]′ (splitAt m i)  ≡⟨ [-,]-cong (++-↑ʳ X Y) (splitAt m i) ⟩
+    [ Y , (X ++ Y) ∘ i₁ ]′ (splitAt m i)              ≡⟨ [,-]-cong (++-↑ˡ X Y) (splitAt m i) ⟩
+    [ Y , X ]′ (splitAt m i)                          ≡⟨⟩
+    (Y ++ X) i                                        ∎
+  where
+    open ≡-Reasoning
+    open Inverse
+    module +-swap = _≅_ (+-comm {m} {n})
+    n+m↔m+n : Permutation (n + m) (m + n)
+    n+m↔m+n .to = +-swap.to
+    n+m↔m+n .from = +-swap.from
+    n+m↔m+n .to-cong ≡.refl = ≡.refl
+    n+m↔m+n .from-cong ≡.refl = ≡.refl
+    n+m↔m+n .inverse = (λ { ≡.refl → +-swap.isoˡ _ }) , (λ { ≡.refl → +-swap.isoʳ _ })
+
+open SymmetricMonoidalFunctor
+Push,++,[] : SymmetricMonoidalFunctor
+Push,++,[] .F = Push
+Push,++,[] .isBraidedMonoidal = record
+    { isMonoidal = record
+        { ε = Push-ε
+        ; ⊗-homo = ⊗-homomorphism
+        ; associativity = λ { {m} {n} {o} {(X , Y) , Z} i → Push-assoc X Y Z i }
+        ; unitaryˡ = λ { {n} {_ , X} i → merge-⁅⁆ X i }
+        ; unitaryʳ = λ { {n} {X , _} i → Push-unitaryʳ X i }
+        }
+    ; braiding-compat = λ { {n} {m} {X , Y} i → Push-swap X Y i }
+    }