{-# OPTIONS --without-K --safe #-}
module Data.Fin.Subset.Properties where
import Algebra.Definitions as AlgebraicDefinitions
import Algebra.Structures as AlgebraicStructures
open import Algebra.Bundles
import Algebra.Properties.Lattice as L
import Algebra.Properties.DistributiveLattice as DL
import Algebra.Properties.BooleanAlgebra as BA
open import Data.Bool.Properties
open import Data.Fin using (Fin; suc; zero)
open import Data.Fin.Subset
open import Data.Fin.Properties using (any?; decFinSubset)
open import Data.Nat.Base using (ℕ; zero; suc; z≤n; s≤s; _≤_)
open import Data.Nat.Properties using (≤-step)
open import Data.Product as Product using (∃; ∄; _×_; _,_)
open import Data.Sum as Sum using (_⊎_; inj₁; inj₂; [_,_]′)
open import Data.Vec
open import Data.Vec.Properties
open import Function.Base using (_∘_; const; id; case_of_)
open import Function.Equivalence using (_⇔_; equivalence)
open import Relation.Binary as B hiding (Decidable)
open import Relation.Binary.PropositionalEquality
using (_≡_; refl; cong; cong₂; subst; isEquivalence)
open import Relation.Nullary using (Dec; yes; no)
import Relation.Nullary.Decidable as Dec
open import Relation.Nullary.Negation using (contradiction)
open import Relation.Nullary.Sum using (_⊎-dec_)
open import Relation.Unary using (Pred; Decidable; Satisfiable)
drop-there : ∀ {s n x} {p : Subset n} → suc x ∈ s ∷ p → x ∈ p
drop-there (there x∈p) = x∈p
drop-∷-⊆ : ∀ {n s₁ s₂} {p₁ p₂ : Subset n} → s₁ ∷ p₁ ⊆ s₂ ∷ p₂ → p₁ ⊆ p₂
drop-∷-⊆ p₁s₁⊆p₂s₂ x∈p₁ = drop-there (p₁s₁⊆p₂s₂ (there x∈p₁))
module _ {n} {p q : Subset n} where
out⊆ : ∀ {y} → p ⊆ q → outside ∷ p ⊆ y ∷ q
out⊆ p⊆q (there ∈p) = there (p⊆q ∈p)
out⊆-⇔ : ∀ {y} → p ⊆ q ⇔ outside ∷ p ⊆ y ∷ q
out⊆-⇔ = equivalence out⊆ drop-∷-⊆
in⊆in : p ⊆ q → inside ∷ p ⊆ inside ∷ q
in⊆in p⊆q here = here
in⊆in p⊆q (there ∈p) = there (p⊆q ∈p)
in⊆in-⇔ : p ⊆ q ⇔ inside ∷ p ⊆ inside ∷ q
in⊆in-⇔ = equivalence in⊆in drop-∷-⊆
infix 4 _∈?_
_∈?_ : ∀ {n} x (p : Subset n) → Dec (x ∈ p)
zero ∈? inside ∷ p = yes here
zero ∈? outside ∷ p = no λ()
suc n ∈? s ∷ p = Dec.map′ there drop-there (n ∈? p)
drop-∷-Empty : ∀ {n s} {p : Subset n} → Empty (s ∷ p) → Empty p
drop-∷-Empty ¬∃∈ (x , x∈p) = ¬∃∈ (suc x , there x∈p)
Empty-unique : ∀ {n} {p : Subset n} → Empty p → p ≡ ⊥
Empty-unique {_} {[]} ¬∃∈ = refl
Empty-unique {_} {inside ∷ p} ¬∃∈ = contradiction (zero , here) ¬∃∈
Empty-unique {_} {outside ∷ p} ¬∃∈ =
cong (outside ∷_) (Empty-unique (drop-∷-Empty ¬∃∈))
nonempty? : ∀ {n} → Decidable (Nonempty {n})
nonempty? p = any? (_∈? p)
-----
∣p∣≤n : ∀ {n} (p : Subset n) → ∣ p ∣ ≤ n
∣p∣≤n = count≤n (_≟ inside)
∉⊥ : ∀ {n} {x : Fin n} → x ∉ ⊥
∉⊥ (there p) = ∉⊥ p
⊥⊆ : ∀ {n} {p : Subset n} → ⊥ ⊆ p
⊥⊆ x∈⊥ = contradiction x∈⊥ ∉⊥
∣⊥∣≡0 : ∀ n → ∣ ⊥ {n = n} ∣ ≡ 0
∣⊥∣≡0 zero = refl
∣⊥∣≡0 (suc n) = ∣⊥∣≡0 n
∈⊤ : ∀ {n} {x : Fin n} → x ∈ ⊤
∈⊤ {x = zero} = here
∈⊤ {x = suc x} = there ∈⊤
⊆⊤ : ∀ {n} {p : Subset n} → p ⊆ ⊤
⊆⊤ = const ∈⊤
∣⊤∣≡n : ∀ n → ∣ ⊤ {n = n} ∣ ≡ n
∣⊤∣≡n zero = refl
∣⊤∣≡n (suc n) = cong suc (∣⊤∣≡n n)
x∈⁅x⁆ : ∀ {n} (x : Fin n) → x ∈ ⁅ x ⁆
x∈⁅x⁆ zero = here
x∈⁅x⁆ (suc x) = there (x∈⁅x⁆ x)
x∈⁅y⁆⇒x≡y : ∀ {n x} (y : Fin n) → x ∈ ⁅ y ⁆ → x ≡ y
x∈⁅y⁆⇒x≡y zero here = refl
x∈⁅y⁆⇒x≡y zero (there p) = contradiction p ∉⊥
x∈⁅y⁆⇒x≡y (suc y) (there p) = cong suc (x∈⁅y⁆⇒x≡y y p)
x∈⁅y⁆⇔x≡y : ∀ {n} {x y : Fin n} → x ∈ ⁅ y ⁆ ⇔ x ≡ y
x∈⁅y⁆⇔x≡y {_} {x} {y} = equivalence
(x∈⁅y⁆⇒x≡y y)
(λ x≡y → subst (λ y → x ∈ ⁅ y ⁆) x≡y (x∈⁅x⁆ x))
∣⁅x⁆∣≡1 : ∀ {n} (i : Fin n) → ∣ ⁅ i ⁆ ∣ ≡ 1
∣⁅x⁆∣≡1 {suc n} zero = cong suc (∣⊥∣≡0 n)
∣⁅x⁆∣≡1 {_} (suc i) = ∣⁅x⁆∣≡1 i
⊆-refl : ∀ {n} → Reflexive (_⊆_ {n})
⊆-refl = id
⊆-reflexive : ∀ {n} → _≡_ ⇒ (_⊆_ {n})
⊆-reflexive refl = ⊆-refl
⊆-trans : ∀ {n} → Transitive (_⊆_ {n})
⊆-trans p⊆q q⊆r x∈p = q⊆r (p⊆q x∈p)
⊆-antisym : ∀ {n} → Antisymmetric _≡_ (_⊆_ {n})
⊆-antisym {i = []} {[]} p⊆q q⊆p = refl
⊆-antisym {i = x ∷ xs} {y ∷ ys} p⊆q q⊆p with x | y
... | inside | inside = cong₂ _∷_ refl (⊆-antisym (drop-∷-⊆ p⊆q) (drop-∷-⊆ q⊆p))
... | inside | outside = contradiction (p⊆q here) λ()
... | outside | inside = contradiction (q⊆p here) λ()
... | outside | outside = cong₂ _∷_ refl (⊆-antisym (drop-∷-⊆ p⊆q) (drop-∷-⊆ q⊆p))
⊆-min : ∀ {n} → Minimum (_⊆_ {n}) ⊥
⊆-min (x ∷ xs) (there v∈⊥) = there (⊆-min xs v∈⊥)
⊆-max : ∀ {n} → Maximum (_⊆_ {n}) ⊤
⊆-max (inside ∷ xs) here = here
⊆-max (x ∷ xs) (there v∈xs) = there (⊆-max xs v∈xs)
infix 4 _⊆?_
_⊆?_ : ∀ {n} → B.Decidable (_⊆_ {n = n})
[] ⊆? [] = yes id
outside ∷ p ⊆? y ∷ q = Dec.map out⊆-⇔ (p ⊆? q)
inside ∷ p ⊆? outside ∷ q = no (λ p⊆q → case (p⊆q here) of λ())
inside ∷ p ⊆? inside ∷ q = Dec.map in⊆in-⇔ (p ⊆? q)
module _ (n : ℕ) where
⊆-isPreorder : IsPreorder _≡_ (_⊆_ {n})
⊆-isPreorder = record
{ isEquivalence = isEquivalence
; reflexive = ⊆-reflexive
; trans = ⊆-trans
}
⊆-preorder : Preorder _ _ _
⊆-preorder = record
{ isPreorder = ⊆-isPreorder
}
⊆-isPartialOrder : IsPartialOrder _≡_ (_⊆_ {n})
⊆-isPartialOrder = record
{ isPreorder = ⊆-isPreorder
; antisym = ⊆-antisym
}
⊆-poset : Poset _ _ _
⊆-poset = record
{ isPartialOrder = ⊆-isPartialOrder
}
p⊆q⇒∣p∣<∣q∣ : ∀ {n} {p q : Subset n} → p ⊆ q → ∣ p ∣ ≤ ∣ q ∣
p⊆q⇒∣p∣<∣q∣ {p = []} {[]} p⊆q = z≤n
p⊆q⇒∣p∣<∣q∣ {p = outside ∷ p} {outside ∷ q} p⊆q = p⊆q⇒∣p∣<∣q∣ (drop-∷-⊆ p⊆q)
p⊆q⇒∣p∣<∣q∣ {p = outside ∷ p} {inside ∷ q} p⊆q = ≤-step (p⊆q⇒∣p∣<∣q∣ (drop-∷-⊆ p⊆q))
p⊆q⇒∣p∣<∣q∣ {p = inside ∷ p} {outside ∷ q} p⊆q = contradiction (p⊆q here) λ()
p⊆q⇒∣p∣<∣q∣ {p = inside ∷ p} {inside ∷ q} p⊆q = s≤s (p⊆q⇒∣p∣<∣q∣ (drop-∷-⊆ p⊆q))
module _ {n : ℕ} where
open AlgebraicDefinitions {A = Subset n} _≡_
∩-assoc : Associative _∩_
∩-assoc = zipWith-assoc ∧-assoc
∩-comm : Commutative _∩_
∩-comm = zipWith-comm ∧-comm
∩-idem : Idempotent _∩_
∩-idem = zipWith-idem ∧-idem
∩-identityˡ : LeftIdentity ⊤ _∩_
∩-identityˡ = zipWith-identityˡ ∧-identityˡ
∩-identityʳ : RightIdentity ⊤ _∩_
∩-identityʳ = zipWith-identityʳ ∧-identityʳ
∩-identity : Identity ⊤ _∩_
∩-identity = ∩-identityˡ , ∩-identityʳ
∩-zeroˡ : LeftZero ⊥ _∩_
∩-zeroˡ = zipWith-zeroˡ ∧-zeroˡ
∩-zeroʳ : RightZero ⊥ _∩_
∩-zeroʳ = zipWith-zeroʳ ∧-zeroʳ
∩-zero : Zero ⊥ _∩_
∩-zero = ∩-zeroˡ , ∩-zeroʳ
∩-inverseˡ : LeftInverse ⊥ ∁ _∩_
∩-inverseˡ = zipWith-inverseˡ ∧-inverseˡ
∩-inverseʳ : RightInverse ⊥ ∁ _∩_
∩-inverseʳ = zipWith-inverseʳ ∧-inverseʳ
∩-inverse : Inverse ⊥ ∁ _∩_
∩-inverse = ∩-inverseˡ , ∩-inverseʳ
module _ (n : ℕ) where
open AlgebraicStructures {A = Subset n} _≡_
∩-isMagma : IsMagma _∩_
∩-isMagma = record
{ isEquivalence = isEquivalence
; ∙-cong = cong₂ _∩_
}
∩-magma : Magma _ _
∩-magma = record
{ isMagma = ∩-isMagma
}
∩-isSemigroup : IsSemigroup _∩_
∩-isSemigroup = record
{ isMagma = ∩-isMagma
; assoc = ∩-assoc
}
∩-semigroup : Semigroup _ _
∩-semigroup = record
{ isSemigroup = ∩-isSemigroup
}
∩-isBand : IsBand _∩_
∩-isBand = record
{ isSemigroup = ∩-isSemigroup
; idem = ∩-idem
}
∩-band : Band _ _
∩-band = record
{ isBand = ∩-isBand
}
∩-isSemilattice : IsSemilattice _∩_
∩-isSemilattice = record
{ isBand = ∩-isBand
; comm = ∩-comm
}
∩-semilattice : Semilattice _ _
∩-semilattice = record
{ isSemilattice = ∩-isSemilattice
}
∩-isMonoid : IsMonoid _∩_ ⊤
∩-isMonoid = record
{ isSemigroup = ∩-isSemigroup
; identity = ∩-identity
}
∩-monoid : Monoid _ _
∩-monoid = record
{ isMonoid = ∩-isMonoid
}
∩-isCommutativeMonoid : IsCommutativeMonoid _∩_ ⊤
∩-isCommutativeMonoid = record
{ isSemigroup = ∩-isSemigroup
; identityˡ = ∩-identityˡ
; comm = ∩-comm
}
∩-commutativeMonoid : CommutativeMonoid _ _
∩-commutativeMonoid = record
{ isCommutativeMonoid = ∩-isCommutativeMonoid
}
∩-isIdempotentCommutativeMonoid : IsIdempotentCommutativeMonoid _∩_ ⊤
∩-isIdempotentCommutativeMonoid = record
{ isCommutativeMonoid = ∩-isCommutativeMonoid
; idem = ∩-idem
}
∩-idempotentCommutativeMonoid : IdempotentCommutativeMonoid _ _
∩-idempotentCommutativeMonoid = record
{ isIdempotentCommutativeMonoid = ∩-isIdempotentCommutativeMonoid
}
p∩q⊆p : ∀ {n} (p q : Subset n) → p ∩ q ⊆ p
p∩q⊆p [] [] x∈p∩q = x∈p∩q
p∩q⊆p (inside ∷ p) (inside ∷ q) here = here
p∩q⊆p (inside ∷ p) (_ ∷ q) (there ∈p∩q) = there (p∩q⊆p p q ∈p∩q)
p∩q⊆p (outside ∷ p) (_ ∷ q) (there ∈p∩q) = there (p∩q⊆p p q ∈p∩q)
p∩q⊆q : ∀ {n} (p q : Subset n) → p ∩ q ⊆ q
p∩q⊆q p q rewrite ∩-comm p q = p∩q⊆p q p
x∈p∩q⁺ : ∀ {n} {p q : Subset n} {x} → x ∈ p × x ∈ q → x ∈ p ∩ q
x∈p∩q⁺ (here , here) = here
x∈p∩q⁺ (there x∈p , there x∈q) = there (x∈p∩q⁺ (x∈p , x∈q))
x∈p∩q⁻ : ∀ {n} (p q : Subset n) {x} → x ∈ p ∩ q → x ∈ p × x ∈ q
x∈p∩q⁻ (inside ∷ p) (inside ∷ q) here = here , here
x∈p∩q⁻ (s ∷ p) (t ∷ q) (there x∈p∩q) =
Product.map there there (x∈p∩q⁻ p q x∈p∩q)
∩⇔× : ∀ {n} {p q : Subset n} {x} → x ∈ p ∩ q ⇔ (x ∈ p × x ∈ q)
∩⇔× = equivalence (x∈p∩q⁻ _ _) x∈p∩q⁺
module _ {n : ℕ} where
open AlgebraicDefinitions {A = Subset n} _≡_
∪-assoc : Associative _∪_
∪-assoc = zipWith-assoc ∨-assoc
∪-comm : Commutative _∪_
∪-comm = zipWith-comm ∨-comm
∪-idem : Idempotent _∪_
∪-idem = zipWith-idem ∨-idem
∪-identityˡ : LeftIdentity ⊥ _∪_
∪-identityˡ = zipWith-identityˡ ∨-identityˡ
∪-identityʳ : RightIdentity ⊥ _∪_
∪-identityʳ = zipWith-identityʳ ∨-identityʳ
∪-identity : Identity ⊥ _∪_
∪-identity = ∪-identityˡ , ∪-identityʳ
∪-zeroˡ : LeftZero ⊤ _∪_
∪-zeroˡ = zipWith-zeroˡ ∨-zeroˡ
∪-zeroʳ : RightZero ⊤ _∪_
∪-zeroʳ = zipWith-zeroʳ ∨-zeroʳ
∪-zero : Zero ⊤ _∪_
∪-zero = ∪-zeroˡ , ∪-zeroʳ
∪-inverseˡ : LeftInverse ⊤ ∁ _∪_
∪-inverseˡ = zipWith-inverseˡ ∨-inverseˡ
∪-inverseʳ : RightInverse ⊤ ∁ _∪_
∪-inverseʳ = zipWith-inverseʳ ∨-inverseʳ
∪-inverse : Inverse ⊤ ∁ _∪_
∪-inverse = ∪-inverseˡ , ∪-inverseʳ
∪-distribˡ-∩ : _∪_ DistributesOverˡ _∩_
∪-distribˡ-∩ = zipWith-distribˡ ∨-distribˡ-∧
∪-distribʳ-∩ : _∪_ DistributesOverʳ _∩_
∪-distribʳ-∩ = zipWith-distribʳ ∨-distribʳ-∧
∪-distrib-∩ : _∪_ DistributesOver _∩_
∪-distrib-∩ = ∪-distribˡ-∩ , ∪-distribʳ-∩
∩-distribˡ-∪ : _∩_ DistributesOverˡ _∪_
∩-distribˡ-∪ = zipWith-distribˡ ∧-distribˡ-∨
∩-distribʳ-∪ : _∩_ DistributesOverʳ _∪_
∩-distribʳ-∪ = zipWith-distribʳ ∧-distribʳ-∨
∩-distrib-∪ : _∩_ DistributesOver _∪_
∩-distrib-∪ = ∩-distribˡ-∪ , ∩-distribʳ-∪
∪-abs-∩ : _∪_ Absorbs _∩_
∪-abs-∩ = zipWith-absorbs ∨-abs-∧
∩-abs-∪ : _∩_ Absorbs _∪_
∩-abs-∪ = zipWith-absorbs ∧-abs-∨
module _ (n : ℕ) where
open AlgebraicStructures {A = Subset n} _≡_
∪-isMagma : IsMagma _∪_
∪-isMagma = record
{ isEquivalence = isEquivalence
; ∙-cong = cong₂ _∪_
}
∪-magma : Magma _ _
∪-magma = record
{ isMagma = ∪-isMagma
}
∪-isSemigroup : IsSemigroup _∪_
∪-isSemigroup = record
{ isMagma = ∪-isMagma
; assoc = ∪-assoc
}
∪-semigroup : Semigroup _ _
∪-semigroup = record
{ isSemigroup = ∪-isSemigroup
}
∪-isBand : IsBand _∪_
∪-isBand = record
{ isSemigroup = ∪-isSemigroup
; idem = ∪-idem
}
∪-band : Band _ _
∪-band = record
{ isBand = ∪-isBand
}
∪-isSemilattice : IsSemilattice _∪_
∪-isSemilattice = record
{ isBand = ∪-isBand
; comm = ∪-comm
}
∪-semilattice : Semilattice _ _
∪-semilattice = record
{ isSemilattice = ∪-isSemilattice
}
∪-isMonoid : IsMonoid _∪_ ⊥
∪-isMonoid = record
{ isSemigroup = ∪-isSemigroup
; identity = ∪-identity
}
∪-monoid : Monoid _ _
∪-monoid = record
{ isMonoid = ∪-isMonoid
}
∪-isCommutativeMonoid : IsCommutativeMonoid _∪_ ⊥
∪-isCommutativeMonoid = record
{ isSemigroup = ∪-isSemigroup
; identityˡ = ∪-identityˡ
; comm = ∪-comm
}
∪-commutativeMonoid : CommutativeMonoid _ _
∪-commutativeMonoid = record
{ isCommutativeMonoid = ∪-isCommutativeMonoid
}
∪-isIdempotentCommutativeMonoid : IsIdempotentCommutativeMonoid _∪_ ⊥
∪-isIdempotentCommutativeMonoid = record
{ isCommutativeMonoid = ∪-isCommutativeMonoid
; idem = ∪-idem
}
∪-idempotentCommutativeMonoid : IdempotentCommutativeMonoid _ _
∪-idempotentCommutativeMonoid = record
{ isIdempotentCommutativeMonoid = ∪-isIdempotentCommutativeMonoid
}
∪-∩-isLattice : IsLattice _∪_ _∩_
∪-∩-isLattice = record
{ isEquivalence = isEquivalence
; ∨-comm = ∪-comm
; ∨-assoc = ∪-assoc
; ∨-cong = cong₂ _∪_
; ∧-comm = ∩-comm
; ∧-assoc = ∩-assoc
; ∧-cong = cong₂ _∩_
; absorptive = ∪-abs-∩ , ∩-abs-∪
}
∪-∩-lattice : Lattice _ _
∪-∩-lattice = record
{ isLattice = ∪-∩-isLattice
}
∪-∩-isDistributiveLattice : IsDistributiveLattice _∪_ _∩_
∪-∩-isDistributiveLattice = record
{ isLattice = ∪-∩-isLattice
; ∨-distribʳ-∧ = ∪-distribʳ-∩
}
∪-∩-distributiveLattice : DistributiveLattice _ _
∪-∩-distributiveLattice = record
{ isDistributiveLattice = ∪-∩-isDistributiveLattice
}
∪-∩-isBooleanAlgebra : IsBooleanAlgebra _∪_ _∩_ ∁ ⊤ ⊥
∪-∩-isBooleanAlgebra = record
{ isDistributiveLattice = ∪-∩-isDistributiveLattice
; ∨-complementʳ = ∪-inverseʳ
; ∧-complementʳ = ∩-inverseʳ
; ¬-cong = cong ∁
}
∪-∩-booleanAlgebra : BooleanAlgebra _ _
∪-∩-booleanAlgebra = record
{ isBooleanAlgebra = ∪-∩-isBooleanAlgebra
}
∩-∪-isLattice : IsLattice _∩_ _∪_
∩-∪-isLattice = L.∧-∨-isLattice ∪-∩-lattice
∩-∪-lattice : Lattice _ _
∩-∪-lattice = L.∧-∨-lattice ∪-∩-lattice
∩-∪-isDistributiveLattice : IsDistributiveLattice _∩_ _∪_
∩-∪-isDistributiveLattice = DL.∧-∨-isDistributiveLattice ∪-∩-distributiveLattice
∩-∪-distributiveLattice : DistributiveLattice _ _
∩-∪-distributiveLattice = DL.∧-∨-distributiveLattice ∪-∩-distributiveLattice
∩-∪-isBooleanAlgebra : IsBooleanAlgebra _∩_ _∪_ ∁ ⊥ ⊤
∩-∪-isBooleanAlgebra = BA.∧-∨-isBooleanAlgebra ∪-∩-booleanAlgebra
∩-∪-booleanAlgebra : BooleanAlgebra _ _
∩-∪-booleanAlgebra = BA.∧-∨-booleanAlgebra ∪-∩-booleanAlgebra
p⊆p∪q : ∀ {n p} (q : Subset n) → p ⊆ p ∪ q
p⊆p∪q (s ∷ q) here = here
p⊆p∪q (s ∷ q) (there x∈p) = there (p⊆p∪q q x∈p)
q⊆p∪q : ∀ {n} (p q : Subset n) → q ⊆ p ∪ q
q⊆p∪q p q rewrite ∪-comm p q = p⊆p∪q p
x∈p∪q⁻ : ∀ {n} (p q : Subset n) {x} → x ∈ p ∪ q → x ∈ p ⊎ x ∈ q
x∈p∪q⁻ (inside ∷ p) (t ∷ q) here = inj₁ here
x∈p∪q⁻ (outside ∷ p) (inside ∷ q) here = inj₂ here
x∈p∪q⁻ (s ∷ p) (t ∷ q) (there x∈p∪q) =
Sum.map there there (x∈p∪q⁻ p q x∈p∪q)
x∈p∪q⁺ : ∀ {n} {p q : Subset n} {x} → x ∈ p ⊎ x ∈ q → x ∈ p ∪ q
x∈p∪q⁺ (inj₁ x∈p) = p⊆p∪q _ x∈p
x∈p∪q⁺ (inj₂ x∈q) = q⊆p∪q _ _ x∈q
∪⇔⊎ : ∀ {n} {p q : Subset n} {x} → x ∈ p ∪ q ⇔ (x ∈ p ⊎ x ∈ q)
∪⇔⊎ = equivalence (x∈p∪q⁻ _ _) x∈p∪q⁺
Lift? : ∀ {n p} {P : Pred (Fin n) p} → Decidable P → Decidable (Lift P)
Lift? P? p = decFinSubset (_∈? p) (λ {x} _ → P? x)
module _ {p} {P : Pred (Subset zero) p} where
∃-Subset-zero : ∃⟨ P ⟩ → P []
∃-Subset-zero ([] , P[]) = P[]
∃-Subset-[]-⇔ : P [] ⇔ ∃⟨ P ⟩
∃-Subset-[]-⇔ = equivalence ([] ,_) ∃-Subset-zero
module _ {p n} {P : Pred (Subset (suc n)) p} where
∃-Subset-suc : ∃⟨ P ⟩ → ∃⟨ P ∘ (inside ∷_) ⟩ ⊎ ∃⟨ P ∘ (outside ∷_) ⟩
∃-Subset-suc (outside ∷ p , Pop) = inj₂ (p , Pop)
∃-Subset-suc ( inside ∷ p , Pip) = inj₁ (p , Pip)
∃-Subset-∷-⇔ : (∃⟨ P ∘ (inside ∷_) ⟩ ⊎ ∃⟨ P ∘ (outside ∷_) ⟩) ⇔ ∃⟨ P ⟩
∃-Subset-∷-⇔ = equivalence
[ Product.map _ id , Product.map _ id ]′
∃-Subset-suc
anySubset? : ∀ {p n} {P : Pred (Subset n) p} → Decidable P → Dec ∃⟨ P ⟩
anySubset? {n = zero} P? = Dec.map ∃-Subset-[]-⇔ (P? [])
anySubset? {n = suc n} P? =
Dec.map ∃-Subset-∷-⇔ (anySubset? (P? ∘ ( inside ∷_)) ⊎-dec
anySubset? (P? ∘ (outside ∷_)))