not

theorem not_not_em (a : Prop) : ¬¬(a ∨ ¬a)

and

theorem and_self_iff {a : Prop} : a ∧ a ↔ a

theorem and_not_self_iff (a : Prop) : a ∧ ¬a ↔ False

theorem not_and_self_iff (a : Prop) : ¬a ∧ a ↔ False

theorem And.imp {a : Prop} {c : Prop} {b : Prop} {d : Prop} (f : a → c) (g : b → d) (h : a ∧ b) : c ∧ d

theorem And.imp_left {a : Prop} {b : Prop} {c : Prop} (h : a → b) : a ∧ c → b ∧ c

theorem And.imp_right {a : Prop} {b : Prop} {c : Prop} (h : a → b) : c ∧ a → c ∧ b

theorem and_congr {a : Prop} {c : Prop} {b : Prop} {d : Prop} (h₁ : a ↔ c) (h₂ : b ↔ d) : a ∧ b ↔ c ∧ d

theorem and_congr_left' {a : Prop} {b : Prop} {c : Prop} (h : a ↔ b) : a ∧ c ↔ b ∧ c

theorem and_congr_right' {b : Prop} {c : Prop} {a : Prop} (h : b ↔ c) : a ∧ b ↔ a ∧ c

theorem not_and_of_not_left {a : Prop} (b : Prop) : ¬a → ¬(a ∧ b)

theorem not_and_of_not_right (a : Prop) {b : Prop} : ¬b → ¬(a ∧ b)

theorem and_congr_right_eq {a : Prop} {b : Prop} {c : Prop} (h : a → b = c) : (a ∧ b) = (a ∧ c)

theorem and_congr_left_eq {c : Prop} {a : Prop} {b : Prop} (h : c → a = b) : (a ∧ c) = (b ∧ c)

theorem and_left_comm {a : Prop} {b : Prop} {c : Prop} : a ∧ b ∧ c ↔ b ∧ a ∧ c

theorem and_right_comm {a : Prop} {b : Prop} {c : Prop} : (a ∧ b) ∧ c ↔ (a ∧ c) ∧ b

theorem and_rotate {a : Prop} {b : Prop} {c : Prop} : a ∧ b ∧ c ↔ b ∧ c ∧ a

theorem and_and_and_comm {a : Prop} {b : Prop} {c : Prop} {d : Prop} : (a ∧ b) ∧ c ∧ d ↔ (a ∧ c) ∧ b ∧ d

theorem and_and_left {a : Prop} {b : Prop} {c : Prop} : a ∧ b ∧ c ↔ (a ∧ b) ∧ a ∧ c

theorem and_and_right {a : Prop} {b : Prop} {c : Prop} : (a ∧ b) ∧ c ↔ (a ∧ c) ∧ b ∧ c

theorem and_iff_left {b : Prop} {a : Prop} (hb : b) : a ∧ b ↔ a

theorem and_iff_right {a : Prop} {b : Prop} (ha : a) : a ∧ b ↔ b

or

theorem or_self_iff {a : Prop} : a ∨ a ↔ a

theorem not_or_intro {a : Prop} {b : Prop} (ha : ¬a) (hb : ¬b) : ¬(a ∨ b)

theorem or_congr {a : Prop} {c : Prop} {b : Prop} {d : Prop} (h₁ : a ↔ c) (h₂ : b ↔ d) : a ∨ b ↔ c ∨ d

theorem or_congr_left {a : Prop} {b : Prop} {c : Prop} (h : a ↔ b) : a ∨ c ↔ b ∨ c

theorem or_congr_right {b : Prop} {c : Prop} {a : Prop} (h : b ↔ c) : a ∨ b ↔ a ∨ c

theorem or_left_comm {a : Prop} {b : Prop} {c : Prop} : a ∨ b ∨ c ↔ b ∨ a ∨ c

theorem or_right_comm {a : Prop} {b : Prop} {c : Prop} : (a ∨ b) ∨ c ↔ (a ∨ c) ∨ b

theorem or_or_or_comm {a : Prop} {b : Prop} {c : Prop} {d : Prop} : (a ∨ b) ∨ c ∨ d ↔ (a ∨ c) ∨ b ∨ d

theorem or_or_distrib_left {a : Prop} {b : Prop} {c : Prop} : a ∨ b ∨ c ↔ (a ∨ b) ∨ a ∨ c

theorem or_or_distrib_right {a : Prop} {b : Prop} {c : Prop} : (a ∨ b) ∨ c ↔ (a ∨ c) ∨ b ∨ c

theorem or_rotate {a : Prop} {b : Prop} {c : Prop} : a ∨ b ∨ c ↔ b ∨ c ∨ a

theorem or_iff_left {b : Prop} {a : Prop} (hb : ¬b) : a ∨ b ↔ a

theorem or_iff_right {a : Prop} {b : Prop} (ha : ¬a) : a ∨ b ↔ b

distributivity

theorem not_imp_of_and_not {a : Prop} {b : Prop} : a ∧ ¬b → ¬(a → b)

theorem imp_and {b : Prop} {c : Prop} {α : Sort u_1} : α → b ∧ c ↔ (α → b) ∧ (α → c)

theorem not_and' {a : Prop} {b : Prop} : ¬(a ∧ b) ↔ b → ¬a

theorem and_or_left {a : Prop} {b : Prop} {c : Prop} : a ∧ (b ∨ c) ↔ a ∧ b ∨ a ∧ c

∧ distributes over ∨ (on the left).

theorem or_and_right {a : Prop} {b : Prop} {c : Prop} : (a ∨ b) ∧ c ↔ a ∧ c ∨ b ∧ c

∧ distributes over ∨ (on the right).

theorem or_and_left {a : Prop} {b : Prop} {c : Prop} : a ∨ b ∧ c ↔ (a ∨ b) ∧ (a ∨ c)

∨ distributes over ∧ (on the left).

theorem and_or_right {a : Prop} {b : Prop} {c : Prop} : a ∧ b ∨ c ↔ (a ∨ c) ∧ (b ∨ c)

∨ distributes over ∧ (on the right).

theorem or_imp {a : Prop} {b : Prop} {c : Prop} : a ∨ b → c ↔ (a → c) ∧ (b → c)

theorem not_or {p : Prop} {q : Prop} : ¬(p ∨ q) ↔ ¬p ∧ ¬q

theorem not_and_of_not_or_not {a : Prop} {b : Prop} (h : ¬a ∨ ¬b) : ¬(a ∧ b)

exists and forall

theorem forall_imp {α : Sort u_1} {p : α → Prop} {q : α → Prop} (h : ∀ (a : α), p a → q a) : (∀ (a : α), p a) → ∀ (a : α), q a

@[simp]

theorem forall_exists_index {α : Sort u_1} {p : α → Prop} {q : (∃ (x : α), p x) → Prop} : (∀ (h : ∃ (x : α), p x), q h) ↔ ∀ (x : α) (h : p x), q ⋯

As simp does not index foralls, this @[simp] lemma is tried on every forall expression. This is not ideal, and likely a performance issue, but it is difficult to remove this attribute at this time.

theorem Exists.imp {α : Sort u_1} {p : α → Prop} {q : α → Prop} (h : ∀ (a : α), p a → q a) : (∃ (a : α), p a) → ∃ (a : α), q a

theorem Exists.imp' {α : Sort u_2} {p : α → Prop} {β : Sort u_1} {q : β → Prop} (f : α → β) (hpq : ∀ (a : α), p a → q (f a)) : (∃ (a : α), p a) → ∃ (b : β), q b

theorem exists_imp {α : Sort u_1} {p : α → Prop} {b : Prop} : (∃ (x : α), p x) → b ↔ ∀ (x : α), p x → b

@[simp]

theorem exists_const {b : Prop} (α : Sort u_1) [i : Nonempty α] : (∃ (x : α), b) ↔ b

theorem forall_congr' {α : Sort u_1} {p : α → Prop} {q : α → Prop} (h : ∀ (a : α), p a ↔ q a) : (∀ (a : α), p a) ↔ ∀ (a : α), q a

theorem exists_congr {α : Sort u_1} {p : α → Prop} {q : α → Prop} (h : ∀ (a : α), p a ↔ q a) : (∃ (a : α), p a) ↔ ∃ (a : α), q a

theorem forall₂_congr {α : Sort u_1} {β : α → Sort u_2} {p : (a : α) → β a → Prop} {q : (a : α) → β a → Prop} (h : ∀ (a : α) (b : β a), p a b ↔ q a b) : (∀ (a : α) (b : β a), p a b) ↔ ∀ (a : α) (b : β a), q a b

theorem exists₂_congr {α : Sort u_1} {β : α → Sort u_2} {p : (a : α) → β a → Prop} {q : (a : α) → β a → Prop} (h : ∀ (a : α) (b : β a), p a b ↔ q a b) : (∃ (a : α), ∃ (b : β a), p a b) ↔ ∃ (a : α), ∃ (b : β a), q a b

theorem forall₃_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {p : (a : α) → (b : β a) → γ a b → Prop} {q : (a : α) → (b : β a) → γ a b → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b), p a b c ↔ q a b c) : (∀ (a : α) (b : β a) (c : γ a b), p a b c) ↔ ∀ (a : α) (b : β a) (c : γ a b), q a b c

theorem exists₃_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {p : (a : α) → (b : β a) → γ a b → Prop} {q : (a : α) → (b : β a) → γ a b → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b), p a b c ↔ q a b c) : (∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), p a b c) ↔ ∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), q a b c

theorem forall₄_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {δ : (a : α) → (b : β a) → γ a b → Sort u_4} {p : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Prop} {q : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c), p a b c d ↔ q a b c d) : (∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c), p a b c d) ↔ ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c), q a b c d

theorem exists₄_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {δ : (a : α) → (b : β a) → γ a b → Sort u_4} {p : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Prop} {q : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c), p a b c d ↔ q a b c d) : (∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), ∃ (d : δ a b c), p a b c d) ↔ ∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), ∃ (d : δ a b c), q a b c d

theorem forall₅_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {δ : (a : α) → (b : β a) → γ a b → Sort u_4} {ε : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Sort u_5} {p : (a : α) → (b : β a) → (c : γ a b) → (d : δ a b c) → ε a b c d → Prop} {q : (a : α) → (b : β a) → (c : γ a b) → (d : δ a b c) → ε a b c d → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c) (e : ε a b c d), p a b c d e ↔ q a b c d e) : (∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c) (e : ε a b c d), p a b c d e) ↔ ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c) (e : ε a b c d), q a b c d e

theorem exists₅_congr {α : Sort u_1} {β : α → Sort u_2} {γ : (a : α) → β a → Sort u_3} {δ : (a : α) → (b : β a) → γ a b → Sort u_4} {ε : (a : α) → (b : β a) → (c : γ a b) → δ a b c → Sort u_5} {p : (a : α) → (b : β a) → (c : γ a b) → (d : δ a b c) → ε a b c d → Prop} {q : (a : α) → (b : β a) → (c : γ a b) → (d : δ a b c) → ε a b c d → Prop} (h : ∀ (a : α) (b : β a) (c : γ a b) (d : δ a b c) (e : ε a b c d), p a b c d e ↔ q a b c d e) : (∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), ∃ (d : δ a b c), ∃ (e : ε a b c d), p a b c d e) ↔ ∃ (a : α), ∃ (b : β a), ∃ (c : γ a b), ∃ (d : δ a b c), ∃ (e : ε a b c d), q a b c d e

@[simp]

theorem not_exists {α : Sort u_1} {p : α → Prop} : (¬∃ (x : α), p x) ↔ ∀ (x : α), ¬p x

theorem forall_and {α : Sort u_1} {p : α → Prop} {q : α → Prop} : (∀ (x : α), p x ∧ q x) ↔ (∀ (x : α), p x) ∧ ∀ (x : α), q x

theorem exists_or {α : Sort u_1} {p : α → Prop} {q : α → Prop} : (∃ (x : α), p x ∨ q x) ↔ (∃ (x : α), p x) ∨ ∃ (x : α), q x

@[simp]

theorem exists_false {α : Sort u_1} : ¬∃ (_a : α), False

@[simp]

theorem forall_const {b : Prop} (α : Sort u_1) [i : Nonempty α] : α → b ↔ b

theorem Exists.nonempty {α : Sort u_1} {p : α → Prop} : (∃ (x : α), p x) → Nonempty α

theorem not_forall_of_exists_not {α : Sort u_1} {p : α → Prop} : (∃ (x : α), ¬p x) → ¬∀ (x : α), p x

@[simp]

theorem forall_eq {α : Sort u_1} {p : α → Prop} {a' : α} : (∀ (a : α), a = a' → p a) ↔ p a'

@[simp]

theorem forall_eq' {α : Sort u_1} {p : α → Prop} {a' : α} : (∀ (a : α), a' = a → p a) ↔ p a'

@[simp]

theorem exists_eq : ∀ {α : Sort u_1} {a' : α}, ∃ (a : α), a = a'

@[simp]

theorem exists_eq' : ∀ {α : Sort u_1} {a' : α}, ∃ (a : α), a' = a

@[simp]

theorem exists_eq_left {α : Sort u_1} {p : α → Prop} {a' : α} : (∃ (a : α), a = a' ∧ p a) ↔ p a'

@[simp]

theorem exists_eq_right {α : Sort u_1} {p : α → Prop} {a' : α} : (∃ (a : α), p a ∧ a = a') ↔ p a'

@[simp]

theorem exists_and_left {α : Sort u_1} {p : α → Prop} {b : Prop} : (∃ (x : α), b ∧ p x) ↔ b ∧ ∃ (x : α), p x

@[simp]

theorem exists_and_right {α : Sort u_1} {p : α → Prop} {b : Prop} : (∃ (x : α), p x ∧ b) ↔ (∃ (x : α), p x) ∧ b

@[simp]

theorem exists_eq_left' {α : Sort u_1} {p : α → Prop} {a' : α} : (∃ (a : α), a' = a ∧ p a) ↔ p a'

@[simp]

theorem forall_eq_or_imp {α : Sort u_1} {p : α → Prop} {q : α → Prop} {a' : α} : (∀ (a : α), a = a' ∨ q a → p a) ↔ p a' ∧ ∀ (a : α), q a → p a

@[simp]

theorem exists_eq_or_imp {α : Sort u_1} {p : α → Prop} {q : α → Prop} {a' : α} : (∃ (a : α), (a = a' ∨ q a) ∧ p a) ↔ p a' ∨ ∃ (a : α), q a ∧ p a

@[simp]

theorem exists_eq_right_right {α : Sort u_1} {p : α → Prop} {q : α → Prop} {a' : α} : (∃ (a : α), p a ∧ q a ∧ a = a') ↔ p a' ∧ q a'

@[simp]

theorem exists_eq_right_right' {α : Sort u_1} {p : α → Prop} {q : α → Prop} {a' : α} : (∃ (a : α), p a ∧ q a ∧ a' = a) ↔ p a' ∧ q a'

@[simp]

theorem exists_prop {b : Prop} {a : Prop} : (∃ (_h : a), b) ↔ a ∧ b

@[simp]

theorem exists_apply_eq_apply {α : Sort u_2} {β : Sort u_1} (f : α → β) (a' : α) : ∃ (a : α), f a = f a'

theorem forall_prop_of_true {p : Prop} {q : p → Prop} (h : p) : (∀ (h' : p), q h') ↔ q h

theorem forall_comm {α : Sort u_2} {β : Sort u_1} {p : α → β → Prop} : (∀ (a : α) (b : β), p a b) ↔ ∀ (b : β) (a : α), p a b

theorem exists_comm {α : Sort u_2} {β : Sort u_1} {p : α → β → Prop} : (∃ (a : α), ∃ (b : β), p a b) ↔ ∃ (b : β), ∃ (a : α), p a b

@[simp]

theorem forall_apply_eq_imp_iff {α : Sort u_2} {β : Sort u_1} {f : α → β} {p : β → Prop} : (∀ (b : β) (a : α), f a = b → p b) ↔ ∀ (a : α), p (f a)

@[simp]

theorem forall_eq_apply_imp_iff {α : Sort u_2} {β : Sort u_1} {f : α → β} {p : β → Prop} : (∀ (b : β) (a : α), b = f a → p b) ↔ ∀ (a : α), p (f a)

@[simp]

theorem forall_apply_eq_imp_iff₂ {α : Sort u_2} {β : Sort u_1} {f : α → β} {p : α → Prop} {q : β → Prop} : (∀ (b : β) (a : α), p a → f a = b → q b) ↔ ∀ (a : α), p a → q (f a)

theorem forall_prop_of_false {p : Prop} {q : p → Prop} (hn : ¬p) : (∀ (h' : p), q h') ↔ True

decidable

theorem Decidable.not_not {p : Prop} [Decidable p] : ¬¬p ↔ p

theorem Decidable.by_contra {p : Prop} [Decidable p] : (¬p → False) → p

def Or.by_cases {p : Prop} {q : Prop} [Decidable p] {α : Sort u} (h : p ∨ q) (h₁ : p → α) (h₂ : q → α) : α

Construct a non-Prop by cases on an Or, when the left conjunct is decidable.

Equations

• Or.by_cases h h₁ h₂ = if hp : p then h₁ hp else h₂ ⋯

def Or.by_cases' {q : Prop} {p : Prop} [Decidable q] {α : Sort u} (h : p ∨ q) (h₁ : p → α) (h₂ : q → α) : α

Construct a non-Prop by cases on an Or, when the right conjunct is decidable.

Equations

• Or.by_cases' h h₁ h₂ = if hq : q then h₂ hq else h₁ ⋯

instance exists_prop_decidable {p : Prop} (P : p → Prop) [Decidable p] [(h : p) → Decidable (P h)] : Decidable (∃ (h : p), P h)

Equations

• exists_prop_decidable P = if h : p then decidable_of_decidable_of_iff ⋯ else isFalse ⋯

instance forall_prop_decidable {p : Prop} (P : p → Prop) [Decidable p] [(h : p) → Decidable (P h)] : Decidable (∀ (h : p), P h)

Equations

• forall_prop_decidable P = if h : p then decidable_of_decidable_of_iff ⋯ else isTrue ⋯

theorem decide_eq_true_iff (p : Prop) [Decidable p] : decide p = true ↔ p

@[simp]

theorem decide_eq_false_iff_not (p : Prop) : ∀ {x : Decidable p}, decide p = false ↔ ¬p

@[simp]

theorem decide_eq_decide {p : Prop} {q : Prop} : ∀ {x : Decidable p} {x_1 : Decidable q}, decide p = decide q ↔ (p ↔ q)

theorem Decidable.of_not_imp {a : Prop} {b : Prop} [Decidable a] (h : ¬(a → b)) : a

theorem Decidable.not_imp_symm {a : Prop} {b : Prop} [Decidable a] (h : ¬a → b) (hb : ¬b) : a

theorem Decidable.not_imp_comm {a : Prop} {b : Prop} [Decidable a] [Decidable b] : ¬a → b ↔ ¬b → a

theorem Decidable.not_imp_self {a : Prop} [Decidable a] : ¬a → a ↔ a

theorem Decidable.or_iff_not_imp_left {a : Prop} {b : Prop} [Decidable a] : a ∨ b ↔ ¬a → b

theorem Decidable.or_iff_not_imp_right {b : Prop} {a : Prop} [Decidable b] : a ∨ b ↔ ¬b → a

theorem Decidable.not_imp_not {a : Prop} {b : Prop} [Decidable a] : ¬a → ¬b ↔ b → a

theorem Decidable.not_or_of_imp {a : Prop} {b : Prop} [Decidable a] (h : a → b) : ¬a ∨ b

theorem Decidable.imp_iff_not_or {a : Prop} {b : Prop} [Decidable a] : a → b ↔ ¬a ∨ b

theorem Decidable.imp_iff_or_not {b : Prop} {a : Prop} [Decidable b] : b → a ↔ a ∨ ¬b

theorem Decidable.imp_or {a : Prop} {b : Prop} {c : Prop} [h : Decidable a] : a → b ∨ c ↔ (a → b) ∨ (a → c)

theorem Decidable.imp_or' {b : Prop} {a : Sort u_1} {c : Prop} [Decidable b] : a → b ∨ c ↔ (a → b) ∨ (a → c)

theorem Decidable.not_imp_iff_and_not {a : Prop} {b : Prop} [Decidable a] : ¬(a → b) ↔ a ∧ ¬b

theorem Decidable.peirce (a : Prop) (b : Prop) [Decidable a] : ((a → b) → a) → a

theorem peirce' {a : Prop} (H : ∀ (b : Prop), (a → b) → a) : a

theorem Decidable.not_iff_not {a : Prop} {b : Prop} [Decidable a] [Decidable b] : (¬a ↔ ¬b) ↔ (a ↔ b)

theorem Decidable.not_iff_comm {a : Prop} {b : Prop} [Decidable a] [Decidable b] : (¬a ↔ b) ↔ (¬b ↔ a)

theorem Decidable.not_iff {b : Prop} {a : Prop} [Decidable b] : ¬(a ↔ b) ↔ (¬a ↔ b)

theorem Decidable.iff_not_comm {a : Prop} {b : Prop} [Decidable a] [Decidable b] : (a ↔ ¬b) ↔ (b ↔ ¬a)

theorem Decidable.iff_iff_and_or_not_and_not {a : Prop} {b : Prop} [Decidable b] : (a ↔ b) ↔ a ∧ b ∨ ¬a ∧ ¬b

theorem Decidable.iff_iff_not_or_and_or_not {a : Prop} {b : Prop} [Decidable a] [Decidable b] : (a ↔ b) ↔ (¬a ∨ b) ∧ (a ∨ ¬b)

theorem Decidable.not_and_not_right {b : Prop} {a : Prop} [Decidable b] : ¬(a ∧ ¬b) ↔ a → b

theorem Decidable.not_and_iff_or_not_not {a : Prop} {b : Prop} [Decidable a] : ¬(a ∧ b) ↔ ¬a ∨ ¬b

theorem Decidable.not_and_iff_or_not_not' {b : Prop} {a : Prop} [Decidable b] : ¬(a ∧ b) ↔ ¬a ∨ ¬b

theorem Decidable.or_iff_not_and_not {a : Prop} {b : Prop} [Decidable a] [Decidable b] : a ∨ b ↔ ¬(¬a ∧ ¬b)

theorem Decidable.and_iff_not_or_not {a : Prop} {b : Prop} [Decidable a] [Decidable b] : a ∧ b ↔ ¬(¬a ∨ ¬b)

theorem Decidable.imp_iff_right_iff {a : Prop} {b : Prop} [Decidable a] : (a → b ↔ b) ↔ a ∨ b

theorem Decidable.and_or_imp {a : Prop} {b : Prop} {c : Prop} [Decidable a] : a ∧ b ∨ (a → c) ↔ a → b ∨ c

theorem Decidable.or_congr_left' {c : Prop} {a : Prop} {b : Prop} [Decidable c] (h : ¬c → (a ↔ b)) : a ∨ c ↔ b ∨ c

theorem Decidable.or_congr_right' {a : Prop} {b : Prop} {c : Prop} [Decidable a] (h : ¬a → (b ↔ c)) : a ∨ b ↔ a ∨ c

@[inline]

def decidable_of_iff {b : Prop} (a : Prop) (h : a ↔ b) [Decidable a] : Decidable b

Transfer decidability of a to decidability of b, if the propositions are equivalent. Important: this function should be used instead of rw on Decidable b, because the kernel will get stuck reducing the usage of propext otherwise, and decide will not work.

Equations

• decidable_of_iff a h = decidable_of_decidable_of_iff h

@[inline]

def decidable_of_iff' {a : Prop} (b : Prop) (h : a ↔ b) [Decidable b] : Decidable a

Transfer decidability of b to decidability of a, if the propositions are equivalent. This is the same as decidable_of_iff but the iff is flipped.

Equations

• decidable_of_iff' b h = decidable_of_decidable_of_iff ⋯

instance Decidable.predToBool {α : Sort u_1} (p : α → Prop) [DecidablePred p] : CoeDep (α → Prop) p (α → Bool)

Equations

• Decidable.predToBool p = { coe := fun (b : α) => decide (p b) }

def decidable_of_bool {a : Prop} (b : Bool) : (b = true ↔ a) → Decidable a

Prove that a is decidable by constructing a boolean b and a proof that b ↔ a. (This is sometimes taken as an alternate definition of decidability.)

Equations

• decidable_of_bool x✝ x = match x✝, x with | true, h => isTrue ⋯ | false, h => isFalse ⋯

theorem Decidable.not_forall {α : Sort u_1} {p : α → Prop} [Decidable (∃ (x : α), ¬p x)] [(x : α) → Decidable (p x)] : (¬∀ (x : α), p x) ↔ ∃ (x : α), ¬p x

theorem Decidable.not_forall_not {α : Sort u_1} {p : α → Prop} [Decidable (∃ (x : α), p x)] : (¬∀ (x : α), ¬p x) ↔ ∃ (x : α), p x

theorem Decidable.not_exists_not {α : Sort u_1} {p : α → Prop} [(x : α) → Decidable (p x)] : (¬∃ (x : α), ¬p x) ↔ ∀ (x : α), p x