The powerset of a finset

powerset

def Finset.powerset {α : Type u_1} (s : Finset α) : Finset (Finset α)

When s is a finset, s.powerset is the finset of all subsets of s (seen as finsets).

@[simp]

theorem Finset.mem_powerset {α : Type u_1} {s t : Finset α} : s ∈ t.powerset ↔ s ⊆ t

@[simp]

theorem Finset.coe_powerset {α : Type u_1} (s : Finset α) : ↑s.powerset = toSet ⁻¹' 𝒫↑s

theorem Finset.empty_mem_powerset {α : Type u_1} (s : Finset α) : ∅ ∈ s.powerset

theorem Finset.mem_powerset_self {α : Type u_1} (s : Finset α) : s ∈ s.powerset

theorem Finset.powerset_nonempty {α : Type u_1} (s : Finset α) : s.powerset.Nonempty

@[simp]

theorem Finset.powerset_mono {α : Type u_1} {s t : Finset α} : s.powerset ⊆ t.powerset ↔ s ⊆ t

theorem Finset.powerset_injective {α : Type u_1} : Function.Injective powerset

@[simp]

theorem Finset.powerset_inj {α : Type u_1} {s t : Finset α} : s.powerset = t.powerset ↔ s = t

@[simp]

theorem Finset.powerset_empty {α : Type u_1} : ∅.powerset = {∅}

@[simp]

theorem Finset.powerset_eq_singleton_empty {α : Type u_1} {s : Finset α} : s.powerset = {∅} ↔ s = ∅

@[simp]

theorem Finset.card_powerset {α : Type u_1} (s : Finset α) : s.powerset.card = 2 ^ s.card

Number of Subsets of a Set

theorem Finset.notMem_of_mem_powerset_of_notMem {α : Type u_1} {s t : Finset α} {a : α} (ht : t ∈ s.powerset) (h : a ∉ s) : a ∉ t

@[deprecated Finset.notMem_of_mem_powerset_of_notMem (since := "2025-05-23")]

theorem Finset.not_mem_of_mem_powerset_of_not_mem {α : Type u_1} {s t : Finset α} {a : α} (ht : t ∈ s.powerset) (h : a ∉ s) : a ∉ t

Alias of Finset.notMem_of_mem_powerset_of_notMem.

theorem Finset.powerset_insert {α : Type u_1} [DecidableEq α] (s : Finset α) (a : α) : (insert a s).powerset = s.powerset ∪ image (insert a) s.powerset

theorem Finset.pairwiseDisjoint_pair_insert {α : Type u_1} {s : Finset α} [DecidableEq α] {a : α} (ha : a ∉ s) : (↑s.powerset).PairwiseDisjoint fun (t : Finset α) => {t, insert a t}

instance Finset.decidableExistsOfDecidableSubsets {α : Type u_1} {s : Finset α} {p : (t : Finset α) → t ⊆ s → Prop} [(t : Finset α) → (h : t ⊆ s) → Decidable (p t h)] : Decidable (∃ (t : Finset α) (h : t ⊆ s), p t h)

For predicate p decidable on subsets, it is decidable whether p holds for any subset.

instance Finset.decidableForallOfDecidableSubsets {α : Type u_1} {s : Finset α} {p : (t : Finset α) → t ⊆ s → Prop} [(t : Finset α) → (h : t ⊆ s) → Decidable (p t h)] : Decidable (∀ (t : Finset α) (h : t ⊆ s), p t h)

For predicate p decidable on subsets, it is decidable whether p holds for every subset.

instance Finset.decidableExistsOfDecidableSubsets' {α : Type u_1} {s : Finset α} {p : Finset α → Prop} [(t : Finset α) → Decidable (p t)] : Decidable (∃ t ⊆ s, p t)

For predicate p decidable on subsets, it is decidable whether p holds for any subset.

instance Finset.decidableForallOfDecidableSubsets' {α : Type u_1} {s : Finset α} {p : Finset α → Prop} [(t : Finset α) → Decidable (p t)] : Decidable (∀ t ⊆ s, p t)

For predicate p decidable on subsets, it is decidable whether p holds for every subset.

def Finset.ssubsets {α : Type u_1} [DecidableEq α] (s : Finset α) : Finset (Finset α)

For s a finset, s.ssubsets is the finset comprising strict subsets of s.

@[simp]

theorem Finset.mem_ssubsets {α : Type u_1} [DecidableEq α] {s t : Finset α} : t ∈ s.ssubsets ↔ t ⊂ s

theorem Finset.empty_mem_ssubsets {α : Type u_1} [DecidableEq α] {s : Finset α} (h : s.Nonempty) : ∅ ∈ s.ssubsets

def Finset.decidableExistsOfDecidableSSubsets {α : Type u_1} [DecidableEq α] {s : Finset α} {p : (t : Finset α) → t ⊂ s → Prop} [(t : Finset α) → (h : t ⊂ s) → Decidable (p t h)] : Decidable (∃ (t : Finset α) (h : t ⊂ s), p t h)

For predicate p decidable on ssubsets, it is decidable whether p holds for any ssubset.

def Finset.decidableForallOfDecidableSSubsets {α : Type u_1} [DecidableEq α] {s : Finset α} {p : (t : Finset α) → t ⊂ s → Prop} [(t : Finset α) → (h : t ⊂ s) → Decidable (p t h)] : Decidable (∀ (t : Finset α) (h : t ⊂ s), p t h)

For predicate p decidable on ssubsets, it is decidable whether p holds for every ssubset.

def Finset.decidableExistsOfDecidableSSubsets' {α : Type u_1} [DecidableEq α] {s : Finset α} {p : Finset α → Prop} (hu : (t : Finset α) → t ⊂ s → Decidable (p t)) : Decidable (∃ (t : Finset α) (_ : t ⊂ s), p t)

A version of Finset.decidableExistsOfDecidableSSubsets with a non-dependent p. Typeclass inference cannot find hu here, so this is not an instance.

def Finset.decidableForallOfDecidableSSubsets' {α : Type u_1} [DecidableEq α] {s : Finset α} {p : Finset α → Prop} (hu : (t : Finset α) → t ⊂ s → Decidable (p t)) : Decidable (∀ t ⊂ s, p t)

A version of Finset.decidableForallOfDecidableSSubsets with a non-dependent p. Typeclass inference cannot find hu here, so this is not an instance.

def Finset.powersetCard {α : Type u_1} (n : ℕ) (s : Finset α) : Finset (Finset α)

Given an integer n and a finset s, then powersetCard n s is the finset of subsets of s of cardinality n.

@[simp]

theorem Finset.mem_powersetCard {α : Type u_1} {n : ℕ} {s t : Finset α} : s ∈ powersetCard n t ↔ s ⊆ t ∧ s.card = n

@[simp]

theorem Finset.powersetCard_mono {α : Type u_1} {n : ℕ} {s t : Finset α} (h : s ⊆ t) : powersetCard n s ⊆ powersetCard n t

@[simp]

theorem Finset.card_powersetCard {α : Type u_1} (n : ℕ) (s : Finset α) : (powersetCard n s).card = s.card.choose n

Formula for the Number of Combinations

@[simp]

theorem Finset.powersetCard_zero {α : Type u_1} (s : Finset α) : powersetCard 0 s = {∅}

theorem Finset.powersetCard_empty_subsingleton {α : Type u_1} (n : ℕ) : (↑(powersetCard n ∅)).Subsingleton

@[simp]

theorem Finset.map_val_val_powersetCard {α : Type u_1} (s : Finset α) (i : ℕ) : Multiset.map val (powersetCard i s).val = Multiset.powersetCard i s.val

theorem Finset.powersetCard_one {α : Type u_1} (s : Finset α) : powersetCard 1 s = map { toFun := singleton, inj' := ⋯ } s

@[simp]

theorem Finset.powersetCard_eq_empty {α : Type u_1} {n : ℕ} {s : Finset α} : powersetCard n s = ∅ ↔ s.card < n

@[simp]

theorem Finset.powersetCard_card_add {α : Type u_1} {n : ℕ} (s : Finset α) (hn : 0 < n) : powersetCard (s.card + n) s = ∅

theorem Finset.powersetCard_eq_filter {α : Type u_1} {n : ℕ} {s : Finset α} : powersetCard n s = filter (fun (x : Finset α) => x.card = n) s.powerset

theorem Finset.powersetCard_succ_insert {α : Type u_1} [DecidableEq α] {x : α} {s : Finset α} (h : x ∉ s) (n : ℕ) : powersetCard n.succ (insert x s) = powersetCard n.succ s ∪ image (insert x) (powersetCard n s)

@[simp]

theorem Finset.powersetCard_nonempty {α : Type u_1} {n : ℕ} {s : Finset α} : (powersetCard n s).Nonempty ↔ n ≤ s.card

theorem Finset.powersetCard_nonempty_of_le {α : Type u_1} {n : ℕ} {s : Finset α} : n ≤ s.card → (powersetCard n s).Nonempty

Alias of the reverse direction of Finset.powersetCard_nonempty.

@[simp]

theorem Finset.powersetCard_self {α : Type u_1} (s : Finset α) : powersetCard s.card s = {s}

theorem Finset.pairwise_disjoint_powersetCard {α : Type u_1} (s : Finset α) : Pairwise fun (i j : ℕ) => Disjoint (powersetCard i s) (powersetCard j s)

theorem Finset.powerset_card_disjiUnion {α : Type u_1} (s : Finset α) : s.powerset = (range (s.card + 1)).disjiUnion (fun (i : ℕ) => powersetCard i s) ⋯

theorem Finset.powerset_card_biUnion {α : Type u_1} [DecidableEq (Finset α)] (s : Finset α) : s.powerset = (range (s.card + 1)).biUnion fun (i : ℕ) => powersetCard i s

theorem Finset.powersetCard_sup {α : Type u_1} [DecidableEq α] (u : Finset α) (n : ℕ) (hn : n < u.card) : (powersetCard n.succ u).sup id = u

theorem Finset.powersetCard_map {α : Type u_1} {β : Type u_2} (f : α ↪ β) (n : ℕ) (s : Finset α) : powersetCard n (map f s) = map (mapEmbedding f).toEmbedding (powersetCard n s)