lean2/library/data/finset/comb.lean
2015-05-11 09:14:48 -07:00

293 lines
11 KiB
Text
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

/-
Copyright (c) 2015 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Leonardo de Moura, Jeremy Avigad
Combinators for finite sets.
-/
import data.finset.basic logic.identities
open list quot subtype decidable perm function
namespace finset
/- image (corresponds to map on list) -/
section image
variables {A B : Type}
variable [h : decidable_eq B]
include h
definition image (f : A → B) (s : finset A) : finset B :=
quot.lift_on s
(λ l, to_finset (list.map f (elt_of l)))
(λ l₁ l₂ p, quot.sound (perm_erase_dup_of_perm (perm_map _ p)))
theorem image_empty (f : A → B) : image f ∅ = ∅ :=
rfl
theorem mem_image_of_mem (f : A → B) {s : finset A} {a : A} : a ∈ s → f a ∈ image f s :=
quot.induction_on s (take l, assume H : a ∈ elt_of l, mem_to_finset (mem_map f H))
theorem mem_image_of_mem_of_eq {f : A → B} {s : finset A} {a : A} {b : B}
(H1 : a ∈ s) (H2 : f a = b) :
b ∈ image f s :=
eq.subst H2 (mem_image_of_mem f H1)
theorem exists_of_mem_image {f : A → B} {s : finset A} {b : B} :
b ∈ image f s → ∃a, a ∈ s ∧ f a = b :=
quot.induction_on s
(take l, assume H : b ∈ erase_dup (list.map f (elt_of l)),
exists_of_mem_map (mem_of_mem_erase_dup H))
theorem mem_image_iff (f : A → B) {s : finset A} {y : B} : y ∈ image f s ↔ ∃x, x ∈ s ∧ f x = y :=
iff.intro exists_of_mem_image
(assume H,
obtain x (H₁ : x ∈ s) (H₂ : f x = y), from H,
mem_image_of_mem_of_eq H₁ H₂)
theorem mem_image_eq (f : A → B) {s : finset A} {y : B} : y ∈ image f s = ∃x, x ∈ s ∧ f x = y :=
propext (mem_image_iff f)
theorem mem_image_of_mem_image_of_subset {f : A → B} {s t : finset A} {y : B}
(H1 : y ∈ image f s) (H2 : s ⊆ t) : y ∈ image f t :=
obtain x (H3: x ∈ s) (H4 : f x = y), from exists_of_mem_image H1,
have H5 : x ∈ t, from mem_of_subset_of_mem H2 H3,
show y ∈ image f t, from mem_image_of_mem_of_eq H5 H4
theorem image_insert [h' : decidable_eq A] (f : A → B) (s : finset A) (a : A) :
image f (insert a s) = insert (f a) (image f s) :=
ext (take y, iff.intro
(assume H : y ∈ image f (insert a s),
obtain x (H1l : x ∈ insert a s) (H1r :f x = y), from exists_of_mem_image H,
have H2 : x = a x ∈ s, from eq_or_mem_of_mem_insert H1l,
or.elim H2
(assume H3 : x = a,
have H4 : f a = y, from eq.subst H3 H1r,
show y ∈ insert (f a) (image f s), from eq.subst H4 !mem_insert)
(assume H3 : x ∈ s,
have H5 : f x ∈ image f s, from mem_image_of_mem f H3,
show y ∈ insert (f a) (image f s), from eq.subst H1r (mem_insert_of_mem _ H5)))
(assume H : y ∈ insert (f a) (image f s),
have H1 : y = f a y ∈ image f s, from eq_or_mem_of_mem_insert H,
or.elim H1
(assume H2 : y = f a,
have H3 : f a ∈ image f (insert a s), from mem_image_of_mem f !mem_insert,
show y ∈ image f (insert a s), from eq.subst (eq.symm H2) H3)
(assume H2 : y ∈ image f s,
show y ∈ image f (insert a s), from mem_image_of_mem_image_of_subset H2 !subset_insert)))
end image
/- filter and set-builder notation -/
section filter
variables {A : Type} [deceq : decidable_eq A]
include deceq
variables (p : A → Prop) [decp : decidable_pred p] (s : finset A) {x : A}
include decp
definition filter : finset A :=
quot.lift_on s
(λl, to_finset_of_nodup
(list.filter p (subtype.elt_of l))
(list.nodup_filter p (subtype.has_property l)))
(λ l₁ l₂ u, quot.sound (perm.perm_filter u))
notation `{` binders ∈ s `|` r:(scoped:1 p, filter p s) `}` := r
theorem filter_empty : filter p ∅ = ∅ := rfl
variables {p s}
theorem of_mem_filter : x ∈ filter p s → p x :=
quot.induction_on s (take l, list.of_mem_filter)
theorem mem_of_mem_filter : x ∈ filter p s → x ∈ s :=
quot.induction_on s (take l, list.mem_of_mem_filter)
theorem mem_filter_of_mem {x : A} : x ∈ s → p x → x ∈ filter p s :=
quot.induction_on s (take l, list.mem_filter_of_mem)
variables (p s)
theorem mem_filter_iff : x ∈ filter p s ↔ x ∈ s ∧ p x :=
iff.intro
(assume H, and.intro (mem_of_mem_filter H) (of_mem_filter H))
(assume H, mem_filter_of_mem (and.left H) (and.right H))
theorem mem_filter_eq : x ∈ filter p s = (x ∈ s ∧ p x) :=
propext !mem_filter_iff
end filter
/- set difference -/
section diff
variables {A : Type} [deceq : decidable_eq A]
include deceq
definition diff (s t : finset A) : finset A := {x ∈ s | x ∉ t}
infix `\`:70 := diff
theorem mem_of_mem_diff {s t : finset A} {x : A} (H : x ∈ s \ t) : x ∈ s :=
mem_of_mem_filter H
theorem not_mem_of_mem_diff {s t : finset A} {x : A} (H : x ∈ s \ t) : x ∉ t :=
of_mem_filter H
theorem mem_diff {s t : finset A} {x : A} (H1 : x ∈ s) (H2 : x ∉ t) : x ∈ s \ t :=
mem_filter_of_mem H1 H2
theorem mem_diff_iff (s t : finset A) (x : A) : x ∈ s \ t ↔ x ∈ s ∧ x ∉ t :=
iff.intro
(assume H, and.intro (mem_of_mem_diff H) (not_mem_of_mem_diff H))
(assume H, mem_diff (and.left H) (and.right H))
theorem mem_diff_eq (s t : finset A) (x : A) : x ∈ s \ t = (x ∈ s ∧ x ∉ t) :=
propext !mem_diff_iff
theorem union_diff_cancel {s t : finset A} (H : s ⊆ t) : s (t \ s) = t :=
ext (take x, iff.intro
(assume H1 : x ∈ s (t \ s),
or.elim (mem_or_mem_of_mem_union H1)
(assume H2 : x ∈ s, mem_of_subset_of_mem H H2)
(assume H2 : x ∈ t \ s, mem_of_mem_diff H2))
(assume H1 : x ∈ t,
decidable.by_cases
(assume H2 : x ∈ s, mem_union_left _ H2)
(assume H2 : x ∉ s, mem_union_right _ (mem_diff H1 H2))))
theorem diff_union_cancel {s t : finset A} (H : s ⊆ t) : (t \ s) s = t :=
eq.subst !union.comm (!union_diff_cancel H)
end diff
/- all -/
section all
variables {A : Type}
definition all (s : finset A) (p : A → Prop) : Prop :=
quot.lift_on s
(λ l, all (elt_of l) p)
(λ l₁ l₂ p, foldr_eq_of_perm (λ a₁ a₂ q, propext !and.left_comm) p true)
theorem all_empty (p : A → Prop) : all ∅ p = true :=
rfl
theorem of_mem_of_all {p : A → Prop} {a : A} {s : finset A} : a ∈ s → all s p → p a :=
quot.induction_on s (λ l i h, list.of_mem_of_all i h)
theorem forall_of_all {p : A → Prop} {s : finset A} (H : all s p) : ∀{a}, a ∈ s → p a :=
λ a H', of_mem_of_all H' H
theorem all_of_forall {p : A → Prop} {s : finset A} : (∀a, a ∈ s → p a) → all s p :=
quot.induction_on s (λ l H, list.all_of_forall H)
theorem all_iff_forall (p : A → Prop) (s : finset A) : all s p ↔ (∀a, a ∈ s → p a) :=
iff.intro forall_of_all all_of_forall
definition decidable_all [instance] (p : A → Prop) [h : decidable_pred p] (s : finset A) :
decidable (all s p) :=
quot.rec_on_subsingleton s (λ l, list.decidable_all p (elt_of l))
theorem all_implies {p q : A → Prop} {s : finset A} : all s p → (∀ x, p x → q x) → all s q :=
quot.induction_on s (λ l h₁ h₂, list.all_implies h₁ h₂)
variable [h : decidable_eq A]
include h
theorem all_union {p : A → Prop} {s₁ s₂ : finset A} : all s₁ p → all s₂ p → all (s₁ s₂) p :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ a₁ a₂, all_union a₁ a₂)
theorem all_of_all_union_left {p : A → Prop} {s₁ s₂ : finset A} : all (s₁ s₂) p → all s₁ p :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ a, list.all_of_all_union_left a)
theorem all_of_all_union_right {p : A → Prop} {s₁ s₂ : finset A} : all (s₁ s₂) p → all s₂ p :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ a, list.all_of_all_union_right a)
theorem all_insert_of_all {p : A → Prop} {a : A} {s : finset A} : p a → all s p → all (insert a s) p :=
quot.induction_on s (λ l h₁ h₂, list.all_insert_of_all h₁ h₂)
theorem all_erase_of_all {p : A → Prop} (a : A) {s : finset A}: all s p → all (erase a s) p :=
quot.induction_on s (λ l h, list.all_erase_of_all a h)
theorem all_inter_of_all_left {p : A → Prop} {s₁ : finset A} (s₂ : finset A) : all s₁ p → all (s₁ ∩ s₂) p :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ h, list.all_inter_of_all_left _ h)
theorem all_inter_of_all_right {p : A → Prop} {s₁ : finset A} (s₂ : finset A) : all s₂ p → all (s₁ ∩ s₂) p :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ h, list.all_inter_of_all_right _ h)
theorem subset_iff_all (s t : finset A) : s ⊆ t ↔ all s (λ x, x ∈ t) :=
iff.intro
(assume H : s ⊆ t, all_of_forall (take x, assume H1, mem_of_subset_of_mem H H1))
(assume H : all s (λ x, x ∈ t), subset_of_forall (take x, assume H1 : x ∈ s, of_mem_of_all H1 H))
definition decidable_subset [instance] (s t : finset A) : decidable (s ⊆ t) :=
decidable_of_decidable_of_iff _ (iff.symm !subset_iff_all)
end all
/- any -/
section any
variables {A : Type}
definition any (s : finset A) (p : A → Prop) : Prop :=
quot.lift_on s
(λ l, any (elt_of l) p)
(λ l₁ l₂ p, foldr_eq_of_perm (λ a₁ a₂ q, propext !or.left_comm) p false)
theorem any_empty (p : A → Prop) : any ∅ p = false := rfl
theorem exists_of_any {p : A → Prop} {s : finset A} : any s p → ∃a, a ∈ s ∧ p a :=
quot.induction_on s (λ l H, list.exists_of_any H)
theorem any_of_mem {p : A → Prop} {s : finset A} {a : A} : a ∈ s → p a → any s p :=
quot.induction_on s (λ l H1 H2, list.any_of_mem H1 H2)
theorem any_of_exists {p : A → Prop} {s : finset A} (H : ∃a, a ∈ s ∧ p a) : any s p :=
obtain a H₁ H₂, from H,
any_of_mem H₁ H₂
theorem any_iff_exists (p : A → Prop) (s : finset A) : any s p ↔ (∃a, a ∈ s ∧ p a) :=
iff.intro exists_of_any any_of_exists
theorem any_of_insert [h : decidable_eq A] {p : A → Prop} (s : finset A) {a : A} (H : p a) :
any (insert a s) p :=
any_of_mem (mem_insert a s) H
theorem any_of_insert_right [h : decidable_eq A] {p : A → Prop} {s : finset A} (a : A) (H : any s p) :
any (insert a s) p :=
obtain b (H₁ : b ∈ s) (H₂ : p b), from exists_of_any H,
any_of_mem (mem_insert_of_mem a H₁) H₂
definition decidable_any [instance] (p : A → Prop) [h : decidable_pred p] (s : finset A) :
decidable (any s p) :=
quot.rec_on_subsingleton s (λ l, list.decidable_any p (elt_of l))
end any
section product
variables {A B : Type}
definition product (s₁ : finset A) (s₂ : finset B) : finset (A × B) :=
quot.lift_on₂ s₁ s₂
(λ l₁ l₂,
to_finset_of_nodup (product (elt_of l₁) (elt_of l₂))
(nodup_product (has_property l₁) (has_property l₂)))
(λ v₁ v₂ w₁ w₂ p₁ p₂, quot.sound (perm_product p₁ p₂))
infix * := product
theorem empty_product (s : finset B) : @empty A * s = ∅ :=
quot.induction_on s (λ l, rfl)
theorem mem_product {a : A} {b : B} {s₁ : finset A} {s₂ : finset B}
: a ∈ s₁ → b ∈ s₂ → (a, b) ∈ s₁ * s₂ :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ i₁ i₂, list.mem_product i₁ i₂)
theorem mem_of_mem_product_left {a : A} {b : B} {s₁ : finset A} {s₂ : finset B}
: (a, b) ∈ s₁ * s₂ → a ∈ s₁ :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ i, list.mem_of_mem_product_left i)
theorem mem_of_mem_product_right {a : A} {b : B} {s₁ : finset A} {s₂ : finset B}
: (a, b) ∈ s₁ * s₂ → b ∈ s₂ :=
quot.induction_on₂ s₁ s₂ (λ l₁ l₂ i, list.mem_of_mem_product_right i)
theorem product_empty (s : finset A) : s * @empty B = ∅ :=
ext (λ p,
match p with
| (a, b) := iff.intro
(λ i, absurd (mem_of_mem_product_right i) !not_mem_empty)
(λ i, absurd i !not_mem_empty)
end)
end product
end finset