mathlib documentation

data.list.nodup_equiv_fin

Isomorphism between fin (length l) and {x // x ∈ l} #

Given a list `l,

source
def list.nodup.nth_le_equiv {α : Type u_1} [decidable_eq α] (l : list α) (H : l.nodup) :
fin l.length ≃ {x // x ∈ l}

If l has no duplicates, then list.nth_le defines a bijection between fin (length l) and the set of elements of l.

Equations
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@[simp]
theorem list.nodup.coe_nth_le_equiv_apply {α : Type u_1} [decidable_eq α] {l : list α} (H : l.nodup) (i : fin l.length) :
↑(⇑(list.nodup.nth_le_equiv l H) i) = l.nth_le ↑i _
source
@[simp]
theorem list.nodup.coe_nth_le_equiv_symm_apply {α : Type u_1} [decidable_eq α] {l : list α} (H : l.nodup) (x : {x // x ∈ l}) :
↑(⇑((list.nodup.nth_le_equiv l H).symm) x) = list.index_of ↑x l
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theorem list.sorted.nth_le_mono {α : Type u_1} [preorder α] {l : list α} (h : list.sorted has_le.le l) :
monotone (λ (i : fin l.length), l.nth_le ↑i _)
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theorem list.sorted.nth_le_strict_mono {α : Type u_1} [preorder α] {l : list α} (h : list.sorted has_lt.lt l) :
strict_mono (λ (i : fin l.length), l.nth_le ↑i _)
source
def list.sorted.nth_le_iso {α : Type u_1} [preorder α] [decidable_eq α] (l : list α) (H : list.sorted has_lt.lt l) :
fin l.length ≃o {x // x ∈ l}

If l is a list sorted w.r.t. (<), then list.nth_le defines an order isomorphism between fin (length l) and the set of elements of l.

Equations
source
@[simp]
theorem list.sorted.coe_nth_le_iso_apply {α : Type u_1} [preorder α] {l : list α} [decidable_eq α] (H : list.sorted has_lt.lt l) {i : fin l.length} :
↑(⇑(list.sorted.nth_le_iso l H) i) = l.nth_le ↑i _
source
@[simp]
theorem list.sorted.coe_nth_le_iso_symm_apply {α : Type u_1} [preorder α] {l : list α} [decidable_eq α] (H : list.sorted has_lt.lt l) {x : {x // x ∈ l}} :
↑(⇑((list.sorted.nth_le_iso l H).symm) x) = list.index_of ↑x l
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theorem list.sublist_of_order_embedding_nth_eq {α : Type u_1} {l l' : list α} (f : ℕ ↪o ℕ) (hf : ∀ (ix : ℕ), l.nth ix = l'.nth (⇑f ix)) :
l <+ l'

If there is f, an order-preserving embedding of ℕ into ℕ such that any element of l found at index ix can be found at index f ix in l', then sublist l l'.

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theorem list.sublist_iff_exists_order_embedding_nth_eq {α : Type u_1} {l l' : list α} :
l <+ l' ↔ ∃ (f : ℕ ↪o ℕ), ∀ (ix : ℕ), l.nth ix = l'.nth (⇑f ix)

A l : list α is sublist l l' for l' : list α iff there is f, an order-preserving embedding of ℕ into ℕ such that any element of l found at index ix can be found at index f ix in l'.

source
theorem list.sublist_iff_exists_fin_order_embedding_nth_le_eq {α : Type u_1} {l l' : list α} :
l <+ l' ↔ ∃ (f : fin l.length ↪o fin l'.length), ∀ (ix : fin l.length), l.nth_le ↑ix _ = l'.nth_le ↑(⇑f ix) _

A l : list α is sublist l l' for l' : list α iff there is f, an order-preserving embedding of fin l.length into fin l'.length such that any element of l found at index ix can be found at index f ix in l'.

source
theorem list.duplicate_iff_exists_distinct_nth_le {α : Type u_1} {l : list α} {x : α} :
list.duplicate x l ↔ ∃ (n : ℕ) (hn : n < l.length) (m : ℕ) (hm : m < l.length) (h : n < m), x = l.nth_le n hn ∧ x = l.nth_le m hm

An element x : α of l : list α is a duplicate iff it can be found at two distinct indices n m : ℕ inside the list l.