332 lines
16 KiB
Agda
332 lines
16 KiB
Agda
open import Lattice
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open import Equivalence
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open import Relation.Nullary using (Dec; ¬_; yes; no)
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module Lattice.AboveBelow {a} (A : Set a)
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(_≈₁_ : A → A → Set a)
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(≈₁-equiv : IsEquivalence A _≈₁_)
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(≈₁-dec : IsDecidable _≈₁_) where
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open import Data.Empty using (⊥-elim)
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open import Data.Product using (_,_)
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open import Data.Nat using (_≤_; ℕ; z≤n; s≤s; suc)
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open import Relation.Binary.PropositionalEquality as Eq using (_≡_; sym; subst; refl)
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import Chain
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open IsEquivalence ≈₁-equiv using () renaming (≈-refl to ≈₁-refl; ≈-sym to ≈₁-sym; ≈-trans to ≈₁-trans)
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data AboveBelow : Set a where
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⊥ : AboveBelow
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⊤ : AboveBelow
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[_] : A → AboveBelow
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data _≈_ : AboveBelow → AboveBelow → Set a where
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≈-⊥-⊥ : ⊥ ≈ ⊥
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≈-⊤-⊤ : ⊤ ≈ ⊤
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≈-lift : ∀ {x y : A} → x ≈₁ y → [ x ] ≈ [ y ]
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≈-refl : ∀ {ab : AboveBelow} → ab ≈ ab
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≈-refl {⊥} = ≈-⊥-⊥
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≈-refl {⊤} = ≈-⊤-⊤
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≈-refl {[ x ]} = ≈-lift ≈₁-refl
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≈-sym : ∀ {ab₁ ab₂ : AboveBelow} → ab₁ ≈ ab₂ → ab₂ ≈ ab₁
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≈-sym ≈-⊥-⊥ = ≈-⊥-⊥
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≈-sym ≈-⊤-⊤ = ≈-⊤-⊤
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≈-sym (≈-lift x≈₁y) = ≈-lift (≈₁-sym x≈₁y)
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≈-trans : ∀ {ab₁ ab₂ ab₃ : AboveBelow} → ab₁ ≈ ab₂ → ab₂ ≈ ab₃ → ab₁ ≈ ab₃
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≈-trans ≈-⊥-⊥ ≈-⊥-⊥ = ≈-⊥-⊥
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≈-trans ≈-⊤-⊤ ≈-⊤-⊤ = ≈-⊤-⊤
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≈-trans (≈-lift a₁≈a₂) (≈-lift a₂≈a₃) = ≈-lift (≈₁-trans a₁≈a₂ a₂≈a₃)
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≈-equiv : IsEquivalence AboveBelow _≈_
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≈-equiv = record
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{ ≈-refl = ≈-refl
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; ≈-sym = ≈-sym
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; ≈-trans = ≈-trans
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}
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≈-dec : IsDecidable _≈_
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≈-dec ⊥ ⊥ = yes ≈-⊥-⊥
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≈-dec ⊤ ⊤ = yes ≈-⊤-⊤
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≈-dec [ x ] [ y ]
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with ≈₁-dec x y
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... | yes x≈y = yes (≈-lift x≈y)
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... | no x̷≈y = no (λ { (≈-lift x≈y) → x̷≈y x≈y })
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≈-dec ⊤ ⊥ = no λ ()
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≈-dec ⊤ [ x ] = no λ ()
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≈-dec ⊥ ⊤ = no λ ()
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≈-dec ⊥ [ x ] = no λ ()
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≈-dec [ x ] ⊥ = no λ ()
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≈-dec [ x ] ⊤ = no λ ()
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module Plain where
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_⊔_ : AboveBelow → AboveBelow → AboveBelow
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⊥ ⊔ x = x
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⊤ ⊔ x = ⊤
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[ x ] ⊔ [ y ] with ≈₁-dec x y
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... | yes _ = [ x ]
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... | no _ = ⊤
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x ⊔ ⊥ = x
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x ⊔ ⊤ = ⊤
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⊤⊔x≡⊤ : ∀ (x : AboveBelow) → ⊤ ⊔ x ≡ ⊤
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⊤⊔x≡⊤ _ = refl
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x⊔⊤≡⊤ : ∀ (x : AboveBelow) → x ⊔ ⊤ ≡ ⊤
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x⊔⊤≡⊤ ⊤ = refl
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x⊔⊤≡⊤ ⊥ = refl
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x⊔⊤≡⊤ [ x ] = refl
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⊥⊔x≡x : ∀ (x : AboveBelow) → ⊥ ⊔ x ≡ x
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⊥⊔x≡x _ = refl
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x⊔⊥≡x : ∀ (x : AboveBelow) → x ⊔ ⊥ ≡ x
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x⊔⊥≡x ⊤ = refl
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x⊔⊥≡x ⊥ = refl
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x⊔⊥≡x [ x ] = refl
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x≈y⇒[x]⊔[y]≡[x] : ∀ {x y : A} → x ≈₁ y → [ x ] ⊔ [ y ] ≡ [ x ]
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x≈y⇒[x]⊔[y]≡[x] {x} {y} x≈₁y
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with ≈₁-dec x y
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... | yes _ = refl
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... | no x̷≈₁y = ⊥-elim (x̷≈₁y x≈₁y)
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x̷≈y⇒[x]⊔[y]≡⊤ : ∀ {x y : A} → ¬ x ≈₁ y → [ x ] ⊔ [ y ] ≡ ⊤
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x̷≈y⇒[x]⊔[y]≡⊤ {x} {y} x̷≈₁y
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with ≈₁-dec x y
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... | yes x≈₁y = ⊥-elim (x̷≈₁y x≈₁y)
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... | no x̷≈₁y = refl
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≈-⊔-cong : ∀ {ab₁ ab₂ ab₃ ab₄} → ab₁ ≈ ab₂ → ab₃ ≈ ab₄ → (ab₁ ⊔ ab₃) ≈ (ab₂ ⊔ ab₄)
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≈-⊔-cong ≈-⊤-⊤ ≈-⊤-⊤ = ≈-⊤-⊤
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≈-⊔-cong ≈-⊤-⊤ ≈-⊥-⊥ = ≈-⊤-⊤
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≈-⊔-cong ≈-⊥-⊥ ≈-⊤-⊤ = ≈-⊤-⊤
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≈-⊔-cong ≈-⊥-⊥ ≈-⊥-⊥ = ≈-⊥-⊥
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≈-⊔-cong ≈-⊥-⊥ (≈-lift x≈y) = ≈-lift x≈y
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≈-⊔-cong (≈-lift x≈y) ≈-⊥-⊥ = ≈-lift x≈y
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≈-⊔-cong ≈-⊤-⊤ (≈-lift x≈y) = ≈-⊤-⊤
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≈-⊔-cong (≈-lift x≈y) ≈-⊤-⊤ = ≈-⊤-⊤
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≈-⊔-cong (≈-lift {a₁} {a₂} a₁≈a₂) (≈-lift {a₃} {a₄} a₃≈a₄)
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with ≈₁-dec a₁ a₃ | ≈₁-dec a₂ a₄
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... | yes a₁≈a₃ | yes a₂≈a₄ = ≈-lift a₁≈a₂
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... | yes a₁≈a₃ | no a₂̷≈a₄ = ⊥-elim (a₂̷≈a₄ (≈₁-trans (≈₁-sym a₁≈a₂) (≈₁-trans (a₁≈a₃) a₃≈a₄)))
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... | no a₁̷≈a₃ | yes a₂≈a₄ = ⊥-elim (a₁̷≈a₃ (≈₁-trans a₁≈a₂ (≈₁-trans a₂≈a₄ (≈₁-sym a₃≈a₄))))
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... | no _ | no _ = ≈-⊤-⊤
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⊔-assoc : ∀ (ab₁ ab₂ ab₃ : AboveBelow) → ((ab₁ ⊔ ab₂) ⊔ ab₃) ≈ (ab₁ ⊔ (ab₂ ⊔ ab₃))
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⊔-assoc ⊤ ab₂ ab₃ = ≈-⊤-⊤
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⊔-assoc ⊥ ab₂ ab₃ = ≈-refl
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⊔-assoc [ x₁ ] ⊤ ab₃ = ≈-⊤-⊤
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⊔-assoc [ x₁ ] ⊥ ab₃ = ≈-refl
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⊔-assoc [ x₁ ] [ x₂ ] ⊤ rewrite x⊔⊤≡⊤ ([ x₁ ] ⊔ [ x₂ ]) = ≈-⊤-⊤
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⊔-assoc [ x₁ ] [ x₂ ] ⊥ rewrite x⊔⊥≡x ([ x₁ ] ⊔ [ x₂ ]) = ≈-refl
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⊔-assoc [ x₁ ] [ x₂ ] [ x₃ ]
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with ≈₁-dec x₂ x₃ | ≈₁-dec x₁ x₂
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... | no x₂̷≈x₃ | no _ rewrite x̷≈y⇒[x]⊔[y]≡⊤ x₂̷≈x₃ = ≈-⊤-⊤
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... | no x₂̷≈x₃ | yes x₁≈x₂ rewrite x̷≈y⇒[x]⊔[y]≡⊤ x₂̷≈x₃
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rewrite x̷≈y⇒[x]⊔[y]≡⊤ λ x₁≈x₃ → x₂̷≈x₃ (≈₁-trans (≈₁-sym x₁≈x₂) x₁≈x₃) = ≈-⊤-⊤
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... | yes x₂≈x₃ | yes x₁≈x₂ rewrite x≈y⇒[x]⊔[y]≡[x] x₂≈x₃
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rewrite x≈y⇒[x]⊔[y]≡[x] x₁≈x₂
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rewrite x≈y⇒[x]⊔[y]≡[x] (≈₁-trans x₁≈x₂ x₂≈x₃) = ≈-refl
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... | yes x₂≈x₃ | no x₁̷≈x₂ rewrite x̷≈y⇒[x]⊔[y]≡⊤ x₁̷≈x₂ = ≈-⊤-⊤
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⊔-comm : ∀ (ab₁ ab₂ : AboveBelow) → (ab₁ ⊔ ab₂) ≈ (ab₂ ⊔ ab₁)
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⊔-comm ⊤ x rewrite x⊔⊤≡⊤ x = ≈-refl
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⊔-comm ⊥ x rewrite x⊔⊥≡x x = ≈-refl
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⊔-comm x ⊤ rewrite x⊔⊤≡⊤ x = ≈-refl
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⊔-comm x ⊥ rewrite x⊔⊥≡x x = ≈-refl
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⊔-comm [ x₁ ] [ x₂ ] with ≈₁-dec x₁ x₂
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... | yes x₁≈x₂ rewrite x≈y⇒[x]⊔[y]≡[x] (≈₁-sym x₁≈x₂) = ≈-lift x₁≈x₂
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... | no x₁̷≈x₂ rewrite x̷≈y⇒[x]⊔[y]≡⊤ λ x₂≈x₁ → (x₁̷≈x₂ (≈₁-sym x₂≈x₁)) = ≈-⊤-⊤
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⊔-idemp : ∀ ab → (ab ⊔ ab) ≈ ab
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⊔-idemp ⊤ = ≈-⊤-⊤
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⊔-idemp ⊥ = ≈-⊥-⊥
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⊔-idemp [ x ] rewrite x≈y⇒[x]⊔[y]≡[x] (≈₁-refl {x}) = ≈-refl
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isJoinSemilattice : IsSemilattice AboveBelow _≈_ _⊔_
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isJoinSemilattice = record
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{ ≈-equiv = ≈-equiv
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; ≈-⊔-cong = ≈-⊔-cong
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; ⊔-assoc = ⊔-assoc
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; ⊔-comm = ⊔-comm
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; ⊔-idemp = ⊔-idemp
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}
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_⊓_ : AboveBelow → AboveBelow → AboveBelow
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⊥ ⊓ x = ⊥
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⊤ ⊓ x = x
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[ x ] ⊓ [ y ] with ≈₁-dec x y
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... | yes _ = [ x ]
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... | no _ = ⊥
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x ⊓ ⊥ = ⊥
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x ⊓ ⊤ = x
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⊥⊓x≡⊥ : ∀ (x : AboveBelow) → ⊥ ⊓ x ≡ ⊥
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⊥⊓x≡⊥ _ = refl
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x⊓⊥≡⊥ : ∀ (x : AboveBelow) → x ⊓ ⊥ ≡ ⊥
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x⊓⊥≡⊥ ⊤ = refl
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x⊓⊥≡⊥ ⊥ = refl
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x⊓⊥≡⊥ [ x ] = refl
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⊤⊓x≡x : ∀ (x : AboveBelow) → ⊤ ⊓ x ≡ x
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⊤⊓x≡x _ = refl
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x⊓⊤≡x : ∀ (x : AboveBelow) → x ⊓ ⊤ ≡ x
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x⊓⊤≡x ⊤ = refl
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x⊓⊤≡x ⊥ = refl
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x⊓⊤≡x [ x ] = refl
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x≈y⇒[x]⊓[y]≡[x] : ∀ {x y : A} → x ≈₁ y → [ x ] ⊓ [ y ] ≡ [ x ]
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x≈y⇒[x]⊓[y]≡[x] {x} {y} x≈₁y
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with ≈₁-dec x y
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... | yes _ = refl
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... | no x̷≈₁y = ⊥-elim (x̷≈₁y x≈₁y)
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x̷≈y⇒[x]⊓[y]≡⊥ : ∀ {x y : A} → ¬ x ≈₁ y → [ x ] ⊓ [ y ] ≡ ⊥
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x̷≈y⇒[x]⊓[y]≡⊥ {x} {y} x̷≈₁y
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with ≈₁-dec x y
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... | yes x≈₁y = ⊥-elim (x̷≈₁y x≈₁y)
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... | no x̷≈₁y = refl
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≈-⊓-cong : ∀ {ab₁ ab₂ ab₃ ab₄} → ab₁ ≈ ab₂ → ab₃ ≈ ab₄ → (ab₁ ⊓ ab₃) ≈ (ab₂ ⊓ ab₄)
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≈-⊓-cong ≈-⊤-⊤ ≈-⊤-⊤ = ≈-⊤-⊤
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≈-⊓-cong ≈-⊤-⊤ ≈-⊥-⊥ = ≈-⊥-⊥
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≈-⊓-cong ≈-⊥-⊥ ≈-⊤-⊤ = ≈-⊥-⊥
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≈-⊓-cong ≈-⊥-⊥ ≈-⊥-⊥ = ≈-⊥-⊥
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≈-⊓-cong ≈-⊤-⊤ (≈-lift x≈y) = ≈-lift x≈y
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≈-⊓-cong (≈-lift x≈y) ≈-⊤-⊤ = ≈-lift x≈y
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≈-⊓-cong ≈-⊥-⊥ (≈-lift x≈y) = ≈-⊥-⊥
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≈-⊓-cong (≈-lift x≈y) ≈-⊥-⊥ = ≈-⊥-⊥
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≈-⊓-cong (≈-lift {a₁} {a₂} a₁≈a₂) (≈-lift {a₃} {a₄} a₃≈a₄)
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with ≈₁-dec a₁ a₃ | ≈₁-dec a₂ a₄
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... | yes a₁≈a₃ | yes a₂≈a₄ = ≈-lift a₁≈a₂
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... | yes a₁≈a₃ | no a₂̷≈a₄ = ⊥-elim (a₂̷≈a₄ (≈₁-trans (≈₁-sym a₁≈a₂) (≈₁-trans (a₁≈a₃) a₃≈a₄)))
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... | no a₁̷≈a₃ | yes a₂≈a₄ = ⊥-elim (a₁̷≈a₃ (≈₁-trans a₁≈a₂ (≈₁-trans a₂≈a₄ (≈₁-sym a₃≈a₄))))
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... | no _ | no _ = ≈-⊥-⊥
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⊓-assoc : ∀ (ab₁ ab₂ ab₃ : AboveBelow) → ((ab₁ ⊓ ab₂) ⊓ ab₃) ≈ (ab₁ ⊓ (ab₂ ⊓ ab₃))
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⊓-assoc ⊥ ab₂ ab₃ = ≈-⊥-⊥
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⊓-assoc ⊤ ab₂ ab₃ = ≈-refl
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⊓-assoc [ x₁ ] ⊥ ab₃ = ≈-⊥-⊥
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⊓-assoc [ x₁ ] ⊤ ab₃ = ≈-refl
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⊓-assoc [ x₁ ] [ x₂ ] ⊥ rewrite x⊓⊥≡⊥ ([ x₁ ] ⊓ [ x₂ ]) = ≈-⊥-⊥
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⊓-assoc [ x₁ ] [ x₂ ] ⊤ rewrite x⊓⊤≡x ([ x₁ ] ⊓ [ x₂ ]) = ≈-refl
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⊓-assoc [ x₁ ] [ x₂ ] [ x₃ ]
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with ≈₁-dec x₂ x₃ | ≈₁-dec x₁ x₂
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... | no x₂̷≈x₃ | no _ rewrite x̷≈y⇒[x]⊓[y]≡⊥ x₂̷≈x₃ = ≈-⊥-⊥
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... | no x₂̷≈x₃ | yes x₁≈x₂ rewrite x̷≈y⇒[x]⊓[y]≡⊥ x₂̷≈x₃
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rewrite x̷≈y⇒[x]⊓[y]≡⊥ λ x₁≈x₃ → x₂̷≈x₃ (≈₁-trans (≈₁-sym x₁≈x₂) x₁≈x₃) = ≈-⊥-⊥
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... | yes x₂≈x₃ | yes x₁≈x₂ rewrite x≈y⇒[x]⊓[y]≡[x] x₂≈x₃
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rewrite x≈y⇒[x]⊓[y]≡[x] x₁≈x₂
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rewrite x≈y⇒[x]⊓[y]≡[x] (≈₁-trans x₁≈x₂ x₂≈x₃) = ≈-refl
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... | yes x₂≈x₃ | no x₁̷≈x₂ rewrite x̷≈y⇒[x]⊓[y]≡⊥ x₁̷≈x₂ = ≈-⊥-⊥
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⊓-comm : ∀ (ab₁ ab₂ : AboveBelow) → (ab₁ ⊓ ab₂) ≈ (ab₂ ⊓ ab₁)
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⊓-comm ⊥ x rewrite x⊓⊥≡⊥ x = ≈-refl
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⊓-comm ⊤ x rewrite x⊓⊤≡x x = ≈-refl
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⊓-comm x ⊥ rewrite x⊓⊥≡⊥ x = ≈-refl
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⊓-comm x ⊤ rewrite x⊓⊤≡x x = ≈-refl
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⊓-comm [ x₁ ] [ x₂ ] with ≈₁-dec x₁ x₂
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... | yes x₁≈x₂ rewrite x≈y⇒[x]⊓[y]≡[x] (≈₁-sym x₁≈x₂) = ≈-lift x₁≈x₂
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... | no x₁̷≈x₂ rewrite x̷≈y⇒[x]⊓[y]≡⊥ λ x₂≈x₁ → (x₁̷≈x₂ (≈₁-sym x₂≈x₁)) = ≈-⊥-⊥
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⊓-idemp : ∀ ab → (ab ⊓ ab) ≈ ab
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⊓-idemp ⊥ = ≈-⊥-⊥
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⊓-idemp ⊤ = ≈-⊤-⊤
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⊓-idemp [ x ] rewrite x≈y⇒[x]⊓[y]≡[x] (≈₁-refl {x}) = ≈-refl
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isMeetSemilattice : IsSemilattice AboveBelow _≈_ _⊓_
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isMeetSemilattice = record
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{ ≈-equiv = ≈-equiv
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; ≈-⊔-cong = ≈-⊓-cong
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; ⊔-assoc = ⊓-assoc
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; ⊔-comm = ⊓-comm
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; ⊔-idemp = ⊓-idemp
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}
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absorb-⊔-⊓ : ∀ (ab₁ ab₂ : AboveBelow) → (ab₁ ⊔ (ab₁ ⊓ ab₂)) ≈ ab₁
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absorb-⊔-⊓ ⊥ ab₂ rewrite ⊥⊓x≡⊥ ab₂ = ≈-⊥-⊥
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absorb-⊔-⊓ ⊤ _ = ≈-⊤-⊤
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absorb-⊔-⊓ [ x ] ⊥ rewrite x⊓⊥≡⊥ [ x ]
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rewrite x⊔⊥≡x [ x ] = ≈-refl
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absorb-⊔-⊓ [ x ] ⊤ rewrite x⊓⊤≡x [ x ] = ⊔-idemp _
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absorb-⊔-⊓ [ x ] [ y ]
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with ≈₁-dec x y
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... | yes x≈y rewrite x≈y⇒[x]⊓[y]≡[x] x≈y = ⊔-idemp _
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... | no x̷≈y rewrite x̷≈y⇒[x]⊓[y]≡⊥ x̷≈y rewrite x⊔⊥≡x [ x ] = ≈-refl
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absorb-⊓-⊔ : ∀ (ab₁ ab₂ : AboveBelow) → (ab₁ ⊓ (ab₁ ⊔ ab₂)) ≈ ab₁
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absorb-⊓-⊔ ⊤ ab₂ rewrite ⊤⊔x≡⊤ ab₂ = ≈-⊤-⊤
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absorb-⊓-⊔ ⊥ _ = ≈-⊥-⊥
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absorb-⊓-⊔ [ x ] ⊤ rewrite x⊔⊤≡⊤ [ x ]
|
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rewrite x⊓⊤≡x [ x ] = ≈-refl
|
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absorb-⊓-⊔ [ x ] ⊥ rewrite x⊔⊥≡x [ x ] = ⊓-idemp _
|
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absorb-⊓-⊔ [ x ] [ y ]
|
||
with ≈₁-dec x y
|
||
... | yes x≈y rewrite x≈y⇒[x]⊔[y]≡[x] x≈y = ⊓-idemp _
|
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... | no x̷≈y rewrite x̷≈y⇒[x]⊔[y]≡⊤ x̷≈y rewrite x⊓⊤≡x [ x ] = ≈-refl
|
||
|
||
|
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isLattice : IsLattice AboveBelow _≈_ _⊔_ _⊓_
|
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isLattice = record
|
||
{ joinSemilattice = isJoinSemilattice
|
||
; meetSemilattice = isMeetSemilattice
|
||
; absorb-⊔-⊓ = absorb-⊔-⊓
|
||
; absorb-⊓-⊔ = absorb-⊓-⊔
|
||
}
|
||
|
||
open IsLattice isLattice using (_≼_; _≺_)
|
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|
||
⊥≺[x] : ∀ (x : A) → ⊥ ≺ [ x ]
|
||
⊥≺[x] x = (≈-refl , λ ())
|
||
|
||
x≺[y]⇒x≡⊥ : ∀ (x : AboveBelow) (y : A) → x ≺ [ y ] → x ≡ ⊥
|
||
x≺[y]⇒x≡⊥ x y ((x⊔[y]≈[y]) , x̷≈[y]) with x
|
||
... | ⊥ = refl
|
||
... | ⊤ with () ← x⊔[y]≈[y]
|
||
... | [ b ] with ≈₁-dec b y
|
||
... | yes b≈y = ⊥-elim (x̷≈[y] (≈-lift b≈y))
|
||
... | no _ with () ← x⊔[y]≈[y]
|
||
|
||
[x]≺⊤ : ∀ (x : A) → [ x ] ≺ ⊤
|
||
[x]≺⊤ x rewrite x⊔⊤≡⊤ [ x ] = (≈-⊤-⊤ , λ ())
|
||
|
||
[x]≺y⇒y≡⊤ : ∀ (x : A) (y : AboveBelow) → [ x ] ≺ y → y ≡ ⊤
|
||
[x]≺y⇒y≡⊤ x y ([x]⊔y≈y , [x]̷≈y) with y
|
||
... | ⊥ with () ← [x]⊔y≈y
|
||
... | ⊤ = refl
|
||
... | [ a ] with ≈₁-dec x a
|
||
... | yes x≈a = ⊥-elim ([x]̷≈y (≈-lift x≈a))
|
||
... | no _ with () ← [x]⊔y≈y
|
||
|
||
open Chain _≈_ ≈-equiv (IsLattice._≺_ isLattice) (IsLattice.≺-cong isLattice)
|
||
|
||
module _ (x : A) where
|
||
longestChain : Chain ⊥ ⊤ 2
|
||
longestChain = step (⊥≺[x] x) ≈-refl (step ([x]≺⊤ x) ≈-⊤-⊤ (done ≈-⊤-⊤))
|
||
|
||
¬-Chain-⊤ : ∀ {ab : AboveBelow} {n : ℕ} → ¬ Chain ⊤ ab (suc n)
|
||
¬-Chain-⊤ {x} (step (⊤⊔x≈x , ⊤̷≈x) _ _) rewrite ⊤⊔x≡⊤ x = ⊥-elim (⊤̷≈x ⊤⊔x≈x)
|
||
|
||
isLongest : ∀ {ab₁ ab₂ : AboveBelow} {n : ℕ} → Chain ab₁ ab₂ n → n ≤ 2
|
||
isLongest (done _) = z≤n
|
||
isLongest (step _ _ (done _)) = s≤s z≤n
|
||
isLongest (step _ _ (step _ _ (done _))) = s≤s (s≤s z≤n)
|
||
isLongest {⊤} c@(step _ _ _) = ⊥-elim (¬-Chain-⊤ c)
|
||
isLongest {[ x ]} (step {_} {y} [x]≺y y≈y' c@(step _ _ _))
|
||
rewrite [x]≺y⇒y≡⊤ x y [x]≺y with ≈-⊤-⊤ ← y≈y' = ⊥-elim (¬-Chain-⊤ c)
|
||
isLongest {⊥} (step {_} {⊥} (_ , ⊥̷≈⊥) _ _) = ⊥-elim (⊥̷≈⊥ ≈-⊥-⊥)
|
||
isLongest {⊥} (step {_} {⊤} _ ≈-⊤-⊤ c@(step _ _ _)) = ⊥-elim (¬-Chain-⊤ c)
|
||
isLongest {⊥} (step {_} {[ x ]} _ (≈-lift _) (step [x]≺y y≈z c@(step _ _ _)))
|
||
rewrite [x]≺y⇒y≡⊤ _ _ [x]≺y with ≈-⊤-⊤ ← y≈z = ⊥-elim (¬-Chain-⊤ c)
|
||
|
||
isFiniteHeightLattice : IsFiniteHeightLattice AboveBelow 2 _≈_ _⊔_ _⊓_
|
||
isFiniteHeightLattice = record
|
||
{ isLattice = isLattice
|
||
; fixedHeight = (((⊥ , ⊤) , longestChain) , isLongest)
|
||
}
|