193 lines
7.3 KiB
Text
193 lines
7.3 KiB
Text
import data.list
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open list setoid quot decidable nat
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namespace finset
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definition eqv {A : Type} (l₁ l₂ : list A) :=
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∀ a, a ∈ l₁ ↔ a ∈ l₂
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infix `~` := eqv
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theorem eqv.refl {A : Type} (l : list A) : l ~ l :=
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λ a, !iff.refl
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theorem eqv.symm {A : Type} {l₁ l₂ : list A} : l₁ ~ l₂ → l₂ ~ l₁ :=
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λ H a, iff.symm (H a)
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theorem eqv.trans {A : Type} {l₁ l₂ l₃ : list A} : l₁ ~ l₂ → l₂ ~ l₃ → l₁ ~ l₃ :=
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λ H₁ H₂ a, iff.trans (H₁ a) (H₂ a)
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theorem eqv.is_equivalence (A : Type) : equivalence (@eqv A) :=
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and.intro (@eqv.refl A) (and.intro (@eqv.symm A) (@eqv.trans A))
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definition norep {A : Type} [H : decidable_eq A] : list A → list A
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| [] := []
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| (x :: xs) := if x ∈ xs then norep xs else x :: norep xs
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definition eqv_norep {A : Type} [H : decidable_eq A] : ∀ l : list A, l ~ norep l
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| [] := (λ a, iff.rfl)
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| (x :: xs) :=
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take y,
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show y ∈ x :: xs ↔ y ∈ if x ∈ xs then norep xs else x :: norep xs,
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begin
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apply (@by_cases (x ∈ xs)),
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begin
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intro xin, rewrite (if_pos xin),
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apply iff.intro,
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{intro yinxxs, apply (or.elim (iff.mp !mem_cons_iff yinxxs)),
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intro yeqx, rewrite -yeqx at xin, exact (iff.mp (eqv_norep xs y) xin),
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intro yeqxs, exact (iff.mp (eqv_norep xs y) yeqxs)},
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{intro yinnrep, show y ∈ x::xs, from or.inr (iff.mp' (eqv_norep xs y) yinnrep)}
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end,
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begin
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intro xnin, rewrite (if_neg xnin),
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apply iff.intro,
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{intro yinxxs, apply (or.elim (iff.mp !mem_cons_iff yinxxs)),
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intro yeqx, rewrite yeqx, apply mem_cons,
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intro yinxs, show y ∈ x:: norep xs, from or.inr (iff.mp (eqv_norep xs y) yinxs)},
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{intro yinxnrep, apply (or.elim (iff.mp !mem_cons_iff yinxnrep)),
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intro yeqx, rewrite yeqx, apply mem_cons,
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intro yinrep, show y ∈ x::xs, from or.inr (iff.mp' (eqv_norep xs y) yinrep)}
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end
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end
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definition sub {A : Type} (l₁ l₂ : list A) := ∀ a, a ∈ l₁ → a ∈ l₂
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infix ⊆ := sub
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theorem eqv_of_sub_of_sub {A : Type} {l₁ l₂ : list A} : l₁ ⊆ l₂ → l₂ ⊆ l₁ → l₁ ~ l₂ :=
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assume h₁ h₂ a, iff.intro (h₁ a) (h₂ a)
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theorem sub_of_eqv_left {A : Type} {l₁ l₂ : list A} : l₁ ~ l₂ → l₁ ⊆ l₂ :=
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assume h₁ a ainl₁, iff.mp (h₁ a) ainl₁
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theorem sub_of_eqv_right {A : Type} {l₁ l₂ : list A} : l₁ ~ l₂ → l₂ ⊆ l₁ :=
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assume h₁ a ainl₂, iff.mp' (h₁ a) ainl₂
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definition sub_of_cons_sub {A : Type} {a : A} {l₁ l₂ : list A} : a :: l₁ ⊆ l₂ → l₁ ⊆ l₂ :=
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assume s, take b, assume binl₁, s b (or.inr binl₁)
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definition decidable_sub [instance] {A : Type} [H : decidable_eq A] : ∀ l₁ l₂ : list A, decidable (l₁ ⊆ l₂)
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| [] ys := inl (λ a h, absurd h !not_mem_nil)
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| (x::xs) ys :=
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if xinys : x ∈ ys then
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match decidable_sub xs ys with
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| (inl xs_sub_ys) := inl (λ y yinxxs, or.elim (iff.mp !mem_cons_iff yinxxs)
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(λ yeqx, by rewrite yeqx; exact xinys)
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(λ yinxs, xs_sub_ys y yinxs))
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| (inr nxs_sub_ys) := inr (λ h, absurd (sub_of_cons_sub h) nxs_sub_ys)
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end
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else
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inr (λ h, absurd (h x !mem_cons) xinys)
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example : [(1 : nat), 2, 3] ⊆ [1,3,4,1,2] :=
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dec_trivial
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definition decidable_eqv [instance] {A : Type} [H : decidable_eq A] : ∀ l₁ l₂ : list A, decidable (l₁ ~ l₂) :=
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take l₁ l₂ : list A,
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match decidable_sub l₁ l₂ with
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| (inl s₁) :=
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match decidable_sub l₂ l₁ with
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| (inl s₂) := inl (eqv_of_sub_of_sub s₁ s₂)
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| (inr n₂) := inr (λ h, absurd (sub_of_eqv_right h) n₂)
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end
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| (inr n₁) := inr (λ h, absurd (sub_of_eqv_left h) n₁)
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end
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example : [(1:nat), 2, 3, 2, 2, 2] ~ [1,3,3,1,2] :=
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dec_trivial
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definition finset_setoid [instance] (A : Type) : setoid (list A) :=
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setoid.mk (@eqv A) (eqv.is_equivalence A)
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definition finset (A : Type) : Type :=
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quot (finset_setoid A)
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definition has_decidable_eq [instance] {A : Type} [H : decidable_eq A] : ∀ s₁ s₂ : finset A, decidable (s₁ = s₂) :=
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take s₁ s₂, quot.rec_on_subsingleton₂ s₁ s₂
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(take l₁ l₂,
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match decidable_eqv l₁ l₂ with
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| inl e := inl (quot.sound e)
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| inr d := inr (λ e, absurd (quot.exact e) d)
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end)
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definition to_finset {A : Type} (l : list A) : finset A :=
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⟦l⟧
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definition mem {A : Type} (a : A) (s : finset A) : Prop :=
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quot.lift_on s
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(λ l : list A, a ∈ l)
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(λ l₁ l₂ r, propext (r a))
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infix ∈ := mem
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theorem mem_list {A : Type} {a : A} {l : list A} : a ∈ l → a ∈ ⟦l⟧ :=
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λ H, H
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definition empty {A : Type} : finset A :=
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⟦nil⟧
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notation `∅` := empty
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definition union {A : Type} (s₁ s₂ : finset A) : finset A :=
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quot.lift_on₂ s₁ s₂
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(λ l₁ l₂ : list A, ⟦l₁ ++ l₂⟧)
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(λ l₁ l₂ l₃ l₄ r₁ r₂,
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begin
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apply quot.sound,
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intro a,
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apply iff.intro,
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begin
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intro inl₁l₂,
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apply (or.elim (mem_or_mem_of_mem_append inl₁l₂)),
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intro inl₁, exact (mem_append_of_mem_or_mem (or.inl (iff.mp (r₁ a) inl₁))),
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intro inl₂, exact (mem_append_of_mem_or_mem (or.inr (iff.mp (r₂ a) inl₂)))
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end,
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begin
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intro inl₃l₄,
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apply (or.elim (mem_or_mem_of_mem_append inl₃l₄)),
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intro inl₃, exact (mem_append_of_mem_or_mem (or.inl (iff.mp' (r₁ a) inl₃))),
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intro inl₄, exact (mem_append_of_mem_or_mem (or.inr (iff.mp' (r₂ a) inl₄)))
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end,
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end)
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infix `∪` := union
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theorem mem_union_left {A : Type} (s₁ s₂ : finset A) (a : A) : a ∈ s₁ → a ∈ s₁ ∪ s₂ :=
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quot.ind₂ (λ l₁ l₂ ainl₁, mem_append_left l₂ ainl₁) s₁ s₂
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theorem mem_union_right {A : Type} (s₁ s₂ : finset A) (a : A) : a ∈ s₂ → a ∈ s₁ ∪ s₂ :=
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quot.ind₂ (λ l₁ l₂ ainl₂, mem_append_right l₁ ainl₂) s₁ s₂
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theorem union_empty {A : Type} (s : finset A) : s ∪ ∅ = s :=
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quot.induction_on s (λ l, quot.sound (λ a, by rewrite append_nil_right))
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theorem empty_union {A : Type} (s : finset A) : ∅ ∪ s = s :=
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quot.induction_on s (λ l, quot.sound (λ a, by rewrite append_nil_left))
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example : to_finset (1::2::nil) ∪ to_finset (2::3::nil) = ⟦1 :: 2 :: 2 :: 3 :: nil⟧ :=
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rfl
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example : to_finset [(1:nat), 1, 2, 3] = to_finset [2, 3, 1, 2, 2, 3] :=
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dec_trivial
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example : to_finset [(1:nat), 1, 4, 2, 3] ≠ to_finset [2, 3, 1, 2, 2, 3] :=
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dec_trivial
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definition clean {A : Type} [H : decidable_eq A] (s : finset A) : finset A :=
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quot.lift_on s (λ l, ⟦norep l⟧)
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(λ l₁ l₂ e, calc
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⟦norep l₁⟧ = ⟦l₁⟧ : quot.sound (eqv_norep l₁)
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... = ⟦l₂⟧ : quot.sound e
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... = ⟦norep l₂⟧ : quot.sound (eqv_norep l₂))
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theorem eq_clean {A : Type} [H : decidable_eq A] : ∀ s : finset A, clean s = s :=
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take s, quot.induction_on s (λ l, eq.symm (quot.sound (eqv_norep l)))
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theorem eq_of_clean_eq_clean {A : Type} [H : decidable_eq A] : ∀ s₁ s₂, clean s₁ = clean s₂ → s₁ = s₂ :=
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take s₁ s₂, by rewrite *eq_clean; intro H; apply H
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example : to_finset [(1:nat), 1, 2, 3] = to_finset [1, 2, 2, 2, 3, 3] :=
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!eq_of_clean_eq_clean rfl
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end finset
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