Documentation

Mathlib.Order.Partition.Equipartition

Finite equipartitions #

This file defines finite equipartitions, the partitions whose parts all are the same size up to a difference of 1.

Main declarations #

An equipartition is a partition whose parts are all the same size, up to a difference of 1.

Equations
  • P.IsEquipartition = (P.parts).EquitableOn Finset.card
Instances For
    theorem Finpartition.isEquipartition_iff_card_parts_eq_average {α : Type u_1} [DecidableEq α] {s : Finset α} (P : Finpartition s) :
    P.IsEquipartition aP.parts, a.card = s.card / P.parts.card a.card = s.card / P.parts.card + 1
    theorem Finpartition.not_isEquipartition {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} :
    ¬P.IsEquipartition aP.parts, bP.parts, b.card + 1 < a.card
    theorem Set.Subsingleton.isEquipartition {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (h : (P.parts).Subsingleton) :
    P.IsEquipartition
    theorem Finpartition.IsEquipartition.card_parts_eq_average {α : Type u_1} [DecidableEq α] {s : Finset α} {t : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) (ht : t P.parts) :
    t.card = s.card / P.parts.card t.card = s.card / P.parts.card + 1
    theorem Finpartition.IsEquipartition.card_part_eq_average_iff {α : Type u_1} [DecidableEq α] {s : Finset α} {t : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) (ht : t P.parts) :
    t.card = s.card / P.parts.card t.card s.card / P.parts.card + 1
    theorem Finpartition.IsEquipartition.average_le_card_part {α : Type u_1} [DecidableEq α] {s : Finset α} {t : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) (ht : t P.parts) :
    s.card / P.parts.card t.card
    theorem Finpartition.IsEquipartition.card_part_le_average_add_one {α : Type u_1} [DecidableEq α] {s : Finset α} {t : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) (ht : t P.parts) :
    t.card s.card / P.parts.card + 1
    theorem Finpartition.IsEquipartition.filter_ne_average_add_one_eq_average {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) :
    Finset.filter (fun (p : Finset α) => ¬p.card = s.card / P.parts.card + 1) P.parts = Finset.filter (fun (p : Finset α) => p.card = s.card / P.parts.card) P.parts
    theorem Finpartition.IsEquipartition.card_large_parts_eq_mod {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) :
    (Finset.filter (fun (p : Finset α) => p.card = s.card / P.parts.card + 1) P.parts).card = s.card % P.parts.card

    An equipartition of a finset with n elements into k parts has n % k parts of size n / k + 1.

    theorem Finpartition.IsEquipartition.card_small_parts_eq_mod {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) :
    (Finset.filter (fun (p : Finset α) => p.card = s.card / P.parts.card) P.parts).card = P.parts.card - s.card % P.parts.card

    An equipartition of a finset with n elements into k parts has n - n % k parts of size n / k.

    theorem Finpartition.IsEquipartition.exists_partsEquiv {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) :
    ∃ (f : { x : Finset α // x P.parts } Fin P.parts.card), ∀ (t : { x : Finset α // x P.parts }), (t).card = s.card / P.parts.card + 1 (f t) < s.card % P.parts.card

    There exists an enumeration of an equipartition's parts where larger parts map to smaller numbers and vice versa.

    theorem Finpartition.IsEquipartition.exists_partPreservingEquiv {α : Type u_1} [DecidableEq α] {s : Finset α} {P : Finpartition s} (hP : P.IsEquipartition) :
    ∃ (f : { x : α // x s } Fin s.card), ∀ (a b : { x : α // x s }), P.part a = P.part b (f a) % P.parts.card = (f b) % P.parts.card

    Given a finset equipartitioned into k parts, its elements can be enumerated such that elements in the same part have congruent indices modulo k.

    Discrete and indiscrete finpartitions #

    theorem Finpartition.bot_isEquipartition {α : Type u_1} [DecidableEq α] (s : Finset α) :
    .IsEquipartition
    theorem Finpartition.top_isEquipartition {α : Type u_1} [DecidableEq α] (s : Finset α) [Decidable (s = )] :
    .IsEquipartition
    theorem Finpartition.indiscrete_isEquipartition {α : Type u_1} [DecidableEq α] (s : Finset α) {hs : s } :
    (Finpartition.indiscrete hs).IsEquipartition