168 lines
5.2 KiB
Text
168 lines
5.2 KiB
Text
/-
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Copyright (c) 2015 Leonardo de Moura. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Module: data.list.comb
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Authors: Leonardo de Moura
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List combinators
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-/
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import data.list.basic
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open nat prod decidable function helper_tactics
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namespace list
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variables {A B C : Type}
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definition map (f : A → B) : list A → list B
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| [] := []
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| (a :: l) := f a :: map l
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theorem map_nil (f : A → B) : map f [] = []
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theorem map_cons (f : A → B) (a : A) (l : list A) : map f (a :: l) = f a :: map f l
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theorem map_id : ∀ l : list A, map id l = l
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| [] := rfl
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| (x::xs) := begin rewrite [map_cons, map_id] end
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theorem map_map (g : B → C) (f : A → B) : ∀ l, map g (map f l) = map (g ∘ f) l
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| [] := rfl
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| (a :: l) :=
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show (g ∘ f) a :: map g (map f l) = map (g ∘ f) (a :: l),
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by rewrite (map_map l)
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theorem len_map (f : A → B) : ∀ l : list A, length (map f l) = length l
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| [] := by esimp
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| (a :: l) :=
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show length (map f l) + 1 = length l + 1,
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by rewrite (len_map l)
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theorem mem_map {A B : Type} (f : A → B) : ∀ {a l}, a ∈ l → f a ∈ map f l
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| a [] i := absurd i !not_mem_nil
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| a (x::xs) i := or.elim (eq_or_mem_of_mem_cons i)
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(λ aeqx : a = x, by rewrite [aeqx, map_cons]; apply mem_cons)
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(λ ainxs : a ∈ xs, or.inr (mem_map ainxs))
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definition map₂ (f : A → B → C) : list A → list B → list C
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| [] _ := []
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| _ [] := []
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| (x::xs) (y::ys) := f x y :: map₂ xs ys
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definition foldl (f : A → B → A) : A → list B → A
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| a [] := a
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| a (b :: l) := foldl (f a b) l
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theorem foldl_nil (f : A → B → A) (a : A) : foldl f a [] = a
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theorem foldl_cons (f : A → B → A) (a : A) (b : B) (l : list B) : foldl f a (b::l) = foldl f (f a b) l
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definition foldr (f : A → B → B) : B → list A → B
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| b [] := b
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| b (a :: l) := f a (foldr b l)
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theorem foldr_nil (f : A → B → B) (b : B) : foldr f b [] = b
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theorem foldr_cons (f : A → B → B) (b : B) (a : A) (l : list A) : foldr f b (a::l) = f a (foldr f b l)
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section foldl_eq_foldr
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-- foldl and foldr coincide when f is commutative and associative
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parameters {α : Type} {f : α → α → α}
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hypothesis (Hcomm : ∀ a b, f a b = f b a)
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hypothesis (Hassoc : ∀ a b c, f (f a b) c = f a (f b c))
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include Hcomm Hassoc
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theorem foldl_eq_of_comm_of_assoc : ∀ a b l, foldl f a (b::l) = f b (foldl f a l)
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| a b nil := Hcomm a b
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| a b (c::l) :=
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begin
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change (foldl f (f (f a b) c) l = f b (foldl f (f a c) l)),
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rewrite -foldl_eq_of_comm_of_assoc,
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change (foldl f (f (f a b) c) l = foldl f (f (f a c) b) l),
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have H₁ : f (f a b) c = f (f a c) b, by rewrite [Hassoc, Hassoc, Hcomm b c],
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rewrite H₁
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end
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theorem foldl_eq_foldr : ∀ a l, foldl f a l = foldr f a l
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| a nil := rfl
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| a (b :: l) :=
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begin
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rewrite foldl_eq_of_comm_of_assoc,
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esimp,
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change (f b (foldl f a l) = f b (foldr f a l)),
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rewrite foldl_eq_foldr
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end
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end foldl_eq_foldr
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theorem foldl_append (f : B → A → B) : ∀ (b : B) (l₁ l₂ : list A), foldl f b (l₁++l₂) = foldl f (foldl f b l₁) l₂
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| b [] l₂ := rfl
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| b (a::l₁) l₂ := by rewrite [append_cons, *foldl_cons, foldl_append]
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theorem foldr_append (f : A → B → B) : ∀ (b : B) (l₁ l₂ : list A), foldr f b (l₁++l₂) = foldr f (foldr f b l₂) l₁
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| b [] l₂ := rfl
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| b (a::l₁) l₂ := by rewrite [append_cons, *foldr_cons, foldr_append]
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definition all (p : A → Prop) (l : list A) : Prop :=
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foldr (λ a r, p a ∧ r) true l
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definition any (p : A → Prop) (l : list A) : Prop :=
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foldr (λ a r, p a ∨ r) false l
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definition decidable_all (p : A → Prop) [H : decidable_pred p] : ∀ l, decidable (all p l)
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| [] := decidable_true
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| (a :: l) :=
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match H a with
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| inl Hp₁ :=
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match decidable_all l with
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| inl Hp₂ := inl (and.intro Hp₁ Hp₂)
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| inr Hn₂ := inr (not_and_of_not_right (p a) Hn₂)
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end
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| inr Hn := inr (not_and_of_not_left (all p l) Hn)
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end
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definition decidable_any (p : A → Prop) [H : decidable_pred p] : ∀ l, decidable (any p l)
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| [] := decidable_false
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| (a :: l) :=
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match H a with
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| inl Hp := inl (or.inl Hp)
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| inr Hn₁ :=
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match decidable_any l with
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| inl Hp₂ := inl (or.inr Hp₂)
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| inr Hn₂ := inr (not_or Hn₁ Hn₂)
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end
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end
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definition zip (l₁ : list A) (l₂ : list B) : list (A × B) :=
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map₂ (λ a b, (a, b)) l₁ l₂
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definition unzip : list (A × B) → list A × list B
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| [] := ([], [])
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| ((a, b) :: l) :=
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match unzip l with
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| (la, lb) := (a :: la, b :: lb)
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end
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theorem unzip_nil : unzip (@nil (A × B)) = ([], [])
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theorem unzip_cons (a : A) (b : B) (l : list (A × B)) :
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unzip ((a, b) :: l) = match unzip l with (la, lb) := (a :: la, b :: lb) end :=
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rfl
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theorem zip_unzip : ∀ (l : list (A × B)), zip (pr₁ (unzip l)) (pr₂ (unzip l)) = l
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| [] := rfl
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| ((a, b) :: l) :=
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begin
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rewrite unzip_cons,
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have r : zip (pr₁ (unzip l)) (pr₂ (unzip l)) = l, from zip_unzip l,
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revert r,
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apply (prod.cases_on (unzip l)),
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intros [la, lb, r],
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rewrite -r
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end
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/- flat -/
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definition flat (l : list (list A)) : list A :=
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foldl append nil l
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end list
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attribute list.decidable_any [instance]
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attribute list.decidable_all [instance]
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