Put the fixed point algorithm code into its own file
Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>
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@ -6,7 +6,7 @@ module Chain {a} {A : Set a}
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(_R_ : A → A → Set a)
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(R-≈-cong : ∀ {a₁ a₁' a₂ a₂'} → a₁ ≈ a₁' → a₂ ≈ a₂' → a₁ R a₂ → a₁' R a₂') where
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open import Data.Nat as Nat using (ℕ; suc; _+_; _≤_)
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open import Data.Nat using (ℕ; suc; _+_; _≤_)
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open import Data.Nat.Properties using (+-comm; m+1+n≰m)
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open import Data.Product using (_×_; Σ; _,_)
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open import Relation.Binary.PropositionalEquality as Eq using (_≡_; refl)
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81
Fixedpoint.agda
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81
Fixedpoint.agda
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@ -0,0 +1,81 @@
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open import Data.Nat as Nat using (ℕ; suc; _+_; _≤_)
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open import Lattice
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module Fixedpoint {a} {A : Set a}
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{h : ℕ}
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{_≈_ : A → A → Set a}
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{_⊔_ : A → A → A} {_⊓_ : A → A → A}
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(decA : IsDecidable _≈_)
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(flA : IsFiniteHeightLattice A h _≈_ _⊔_ _⊓_)
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(f : A → A)
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(Monotonicᶠ : Monotonic (IsFiniteHeightLattice._≼_ flA)
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(IsFiniteHeightLattice._≼_ flA) f) where
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open import Data.Nat.Properties using (+-suc; +-comm)
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open import Data.Product using (_×_; Σ; _,_; proj₁; proj₂)
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open import Relation.Binary.PropositionalEquality using (_≡_; sym)
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open import Relation.Nullary using (Dec; ¬_; yes; no)
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import Chain
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module ChainA = Chain _≈_ ≈-equiv _≺_ ≺-cong
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open IsDecidable decA using () renaming (R-dec to ≈-dec)
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open IsFiniteHeightLattice flA
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private
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⊥ᴬ : A
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⊥ᴬ = proj₁ (proj₁ (proj₁ fixedHeight))
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⊥ᴬ≼ : ∀ (a : A) → ⊥ᴬ ≼ a
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⊥ᴬ≼ a with ≈-dec a ⊥ᴬ
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... | yes a≈⊥ᴬ = ≼-cong a≈⊥ᴬ ≈-refl (≼-refl a)
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... | no a̷≈⊥ᴬ with ≈-dec ⊥ᴬ (a ⊓ ⊥ᴬ)
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... | yes ⊥ᴬ≈a⊓⊥ᴬ = (a , ≈-trans (⊔-comm ⊥ᴬ a) (≈-trans (≈-⊔-cong (≈-refl {a}) ⊥ᴬ≈a⊓⊥ᴬ) (absorb-⊔-⊓ a ⊥ᴬ)))
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... | no ⊥ᴬ̷≈a⊓⊥ᴬ = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) (ChainA.step x≺⊥ᴬ ≈-refl (proj₂ (proj₁ fixedHeight))))
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where
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⊥ᴬ⊓a̷≈⊥ᴬ : ¬ (⊥ᴬ ⊓ a) ≈ ⊥ᴬ
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⊥ᴬ⊓a̷≈⊥ᴬ = λ ⊥ᴬ⊓a≈⊥ᴬ → ⊥ᴬ̷≈a⊓⊥ᴬ (≈-trans (≈-sym ⊥ᴬ⊓a≈⊥ᴬ) (⊓-comm _ _))
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x≺⊥ᴬ : (⊥ᴬ ⊓ a) ≺ ⊥ᴬ
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x≺⊥ᴬ = ((⊥ᴬ , ≈-trans (⊔-comm _ _) (≈-trans (≈-refl {⊥ᴬ ⊔ (⊥ᴬ ⊓ a)}) (absorb-⊔-⊓ ⊥ᴬ a))) , ⊥ᴬ⊓a̷≈⊥ᴬ)
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-- using 'g', for gas, here helps make sure the function terminates.
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-- since A forms a fixed-height lattice, we must find a solution after
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-- 'h' steps at most. Gas is set up such that as soon as it runs
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-- out, we have exceeded h steps, which shouldn't be possible.
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doStep : ∀ (g hᶜ : ℕ) (a₁ a₂ : A) (c : ChainA.Chain a₁ a₂ hᶜ) (g+hᶜ≡h : g + hᶜ ≡ suc h) (a₂≼fa₂ : a₂ ≼ f a₂) → Σ A (λ a → a ≈ f a)
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doStep 0 hᶜ a₁ a₂ c g+hᶜ≡sh a₂≼fa₂ rewrite g+hᶜ≡sh = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) c)
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doStep (suc g') hᶜ a₁ a₂ c g+hᶜ≡sh a₂≼fa₂ rewrite sym (+-suc g' hᶜ)
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with ≈-dec a₂ (f a₂)
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... | yes a₂≈fa₂ = (a₂ , a₂≈fa₂)
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... | no a₂̷≈fa₂ = doStep g' (suc hᶜ) a₁ (f a₂) c' g+hᶜ≡sh (Monotonicᶠ a₂≼fa₂)
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where
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a₂≺fa₂ : a₂ ≺ f a₂
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a₂≺fa₂ = (a₂≼fa₂ , a₂̷≈fa₂)
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c' : ChainA.Chain a₁ (f a₂) (suc hᶜ)
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c' rewrite +-comm 1 hᶜ = ChainA.concat c (ChainA.step a₂≺fa₂ ≈-refl (ChainA.done (≈-refl {f a₂})))
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fix : Σ A (λ a → a ≈ f a)
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fix = doStep (suc h) 0 ⊥ᴬ ⊥ᴬ (ChainA.done ≈-refl) (+-comm (suc h) 0) (⊥ᴬ≼ (f ⊥ᴬ))
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aᶠ : A
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aᶠ = proj₁ fix
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aᶠ≈faᶠ : aᶠ ≈ f aᶠ
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aᶠ≈faᶠ = proj₂ fix
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private
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stepPreservesLess : ∀ (g hᶜ : ℕ) (a₁ a₂ a : A) (a≈fa : a ≈ f a) (a₂≼a : a₂ ≼ a)
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(c : ChainA.Chain a₁ a₂ hᶜ) (g+hᶜ≡h : g + hᶜ ≡ suc h)
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(a₂≼fa₂ : a₂ ≼ f a₂) →
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proj₁ (doStep g hᶜ a₁ a₂ c g+hᶜ≡h a₂≼fa₂) ≼ a
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stepPreservesLess 0 _ _ _ _ _ _ c g+hᶜ≡sh _ rewrite g+hᶜ≡sh = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) c)
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stepPreservesLess (suc g') hᶜ a₁ a₂ a a≈fa a₂≼a c g+hᶜ≡sh a₂≼fa₂ rewrite sym (+-suc g' hᶜ)
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with ≈-dec a₂ (f a₂)
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... | yes _ = a₂≼a
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... | no _ = stepPreservesLess g' _ _ _ a a≈fa (≼-cong ≈-refl (≈-sym a≈fa) (Monotonicᶠ a₂≼a)) _ _ _
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aᶠ≼ : ∀ (a : A) → a ≈ f a → aᶠ ≼ a
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aᶠ≼ a a≈fa = stepPreservesLess (suc h) 0 ⊥ᴬ ⊥ᴬ a a≈fa (⊥ᴬ≼ a) (ChainA.done ≈-refl) (+-comm (suc h) 0) (⊥ᴬ≼ (f ⊥ᴬ))
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95
Lattice.agda
95
Lattice.agda
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@ -442,98 +442,3 @@ module IsFiniteHeightLatticeInstances where
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(proj₂ (IsFiniteHeightLattice.fixedHeight lB) b₁b₂))
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)
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}
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module FixedHeightLatticeIsBounded {a} {A : Set a} {h : ℕ}
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{_≈_ : A → A → Set a}
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{_⊔_ : A → A → A} {_⊓_ : A → A → A}
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(decA : IsDecidable _≈_)
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(lA : IsFiniteHeightLattice A h _≈_ _⊔_ _⊓_) where
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open IsFiniteHeightLattice lA using (_≼_; _≺_; fixedHeight; ≈-equiv; ≈-refl; ≈-sym; ≈-trans; ≼-refl; ≼-cong; ≺-cong; ≈-⊔-cong; absorb-⊔-⊓; ⊔-comm; ⊓-comm)
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open IsDecidable decA using () renaming (R-dec to ≈-dec)
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open NatProps using (+-comm; m+1+n≰m)
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private
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module ChainA = Chain _≈_ ≈-equiv _≺_ ≺-cong
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A-BoundedBelow : Σ A (λ ⊥ᴬ → ∀ (a : A) → ⊥ᴬ ≼ a)
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A-BoundedBelow = (⊥ᴬ , ⊥ᴬ≼)
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where
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⊥ᴬ : A
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⊥ᴬ = proj₁ (proj₁ (proj₁ fixedHeight))
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⊥ᴬ≼ : ∀ (a : A) → ⊥ᴬ ≼ a
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⊥ᴬ≼ a
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with ≈-dec a ⊥ᴬ
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... | yes a≈⊥ᴬ = ≼-cong a≈⊥ᴬ ≈-refl (≼-refl a)
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... | no a̷≈⊥ᴬ with ≈-dec ⊥ᴬ (a ⊓ ⊥ᴬ)
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... | yes ⊥ᴬ≈a⊓⊥ᴬ = (a , ≈-trans (⊔-comm ⊥ᴬ a) (≈-trans (≈-⊔-cong (≈-refl {a}) ⊥ᴬ≈a⊓⊥ᴬ) (absorb-⊔-⊓ a ⊥ᴬ)))
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... | no ⊥ᴬ̷≈a⊓⊥ᴬ = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) (ChainA.step x≺⊥ᴬ ≈-refl (proj₂ (proj₁ fixedHeight))))
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where
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⊥ᴬ⊓a̷≈⊥ᴬ : ¬ (⊥ᴬ ⊓ a) ≈ ⊥ᴬ
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⊥ᴬ⊓a̷≈⊥ᴬ = λ ⊥ᴬ⊓a≈⊥ᴬ → ⊥ᴬ̷≈a⊓⊥ᴬ (≈-trans (≈-sym ⊥ᴬ⊓a≈⊥ᴬ) (⊓-comm _ _))
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x≺⊥ᴬ : (⊥ᴬ ⊓ a) ≺ ⊥ᴬ
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x≺⊥ᴬ = ((⊥ᴬ , ≈-trans (⊔-comm _ _) (≈-trans (≈-refl {⊥ᴬ ⊔ (⊥ᴬ ⊓ a)}) (absorb-⊔-⊓ ⊥ᴬ a))) , ⊥ᴬ⊓a̷≈⊥ᴬ)
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module FixedPoint {a} {A : Set a}
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(h : ℕ)
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(_≈_ : A → A → Set a) (decA : IsDecidable _≈_)
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(_⊔_ : A → A → A) (_⊓_ : A → A → A)
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(isFiniteHeightLattice : IsFiniteHeightLattice A h _≈_ _⊔_ _⊓_)
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(f : A → A) (Monotonicᶠ : Monotonic (IsFiniteHeightLattice._≼_ isFiniteHeightLattice)
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(IsFiniteHeightLattice._≼_ isFiniteHeightLattice) f) where
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open IsDecidable decA using () renaming (R-dec to ≈-dec)
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open IsFiniteHeightLattice isFiniteHeightLattice
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open FixedHeightLatticeIsBounded decA isFiniteHeightLattice
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open NatProps using (+-suc; +-comm)
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module ChainA = Chain _≈_ ≈-equiv _≺_ ≺-cong
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private
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⊥ᴬ : A
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⊥ᴬ = proj₁ A-BoundedBelow
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⊥ᴬ≼ : ∀ (a : A) → ⊥ᴬ ≼ a
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⊥ᴬ≼ = proj₂ A-BoundedBelow
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-- using 'g', for gas, here helps make sure the function terminates.
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-- since A forms a fixed-height lattice, we must find a solution after
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-- 'h' steps at most. Gas is set up such that as soon as it runs
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-- out, we have exceeded h steps, which shouldn't be possible.
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doStep : ∀ (g hᶜ : ℕ) (a₁ a₂ : A) (c : ChainA.Chain a₁ a₂ hᶜ) (g+hᶜ≡h : g + hᶜ ≡ suc h) (a₂≼fa₂ : a₂ ≼ f a₂) → Σ A (λ a → a ≈ f a)
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doStep 0 hᶜ a₁ a₂ c g+hᶜ≡sh a₂≼fa₂ rewrite g+hᶜ≡sh = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) c)
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doStep (suc g') hᶜ a₁ a₂ c g+hᶜ≡sh a₂≼fa₂ rewrite sym (+-suc g' hᶜ)
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with ≈-dec a₂ (f a₂)
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... | yes a₂≈fa₂ = (a₂ , a₂≈fa₂)
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... | no a₂̷≈fa₂ = doStep g' (suc hᶜ) a₁ (f a₂) c' g+hᶜ≡sh (Monotonicᶠ a₂≼fa₂)
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where
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a₂≺fa₂ : a₂ ≺ f a₂
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a₂≺fa₂ = (a₂≼fa₂ , a₂̷≈fa₂)
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c' : ChainA.Chain a₁ (f a₂) (suc hᶜ)
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c' rewrite +-comm 1 hᶜ = ChainA.concat c (ChainA.step a₂≺fa₂ ≈-refl (ChainA.done (≈-refl {f a₂})))
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fix : Σ A (λ a → a ≈ f a)
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fix = doStep (suc h) 0 ⊥ᴬ ⊥ᴬ (ChainA.done ≈-refl) (+-comm (suc h) 0) (⊥ᴬ≼ (f ⊥ᴬ))
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aᶠ : A
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aᶠ = proj₁ fix
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aᶠ≈faᶠ : aᶠ ≈ f aᶠ
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aᶠ≈faᶠ = proj₂ fix
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private
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stepPreservesLess : ∀ (g hᶜ : ℕ) (a₁ a₂ a : A) (a≈fa : a ≈ f a) (a₂≼a : a₂ ≼ a)
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(c : ChainA.Chain a₁ a₂ hᶜ) (g+hᶜ≡h : g + hᶜ ≡ suc h)
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(a₂≼fa₂ : a₂ ≼ f a₂) →
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proj₁ (doStep g hᶜ a₁ a₂ c g+hᶜ≡h a₂≼fa₂) ≼ a
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stepPreservesLess 0 _ _ _ _ _ _ c g+hᶜ≡sh _ rewrite g+hᶜ≡sh = absurd (ChainA.Bounded-suc-n (proj₂ fixedHeight) c)
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stepPreservesLess (suc g') hᶜ a₁ a₂ a a≈fa a₂≼a c g+hᶜ≡sh a₂≼fa₂ rewrite sym (+-suc g' hᶜ)
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with ≈-dec a₂ (f a₂)
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... | yes _ = a₂≼a
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... | no _ = stepPreservesLess g' _ _ _ a a≈fa (≼-cong ≈-refl (≈-sym a≈fa) (Monotonicᶠ a₂≼a)) _ _ _
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aᶠ≼ : ∀ (a : A) → a ≈ f a → aᶠ ≼ a
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aᶠ≼ a a≈fa = stepPreservesLess (suc h) 0 ⊥ᴬ ⊥ᴬ a a≈fa (⊥ᴬ≼ a) (ChainA.done ≈-refl) (+-comm (suc h) 0) (⊥ᴬ≼ (f ⊥ᴬ))
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