Note about Mathlib/Init/

The files in Mathlib/Init are leftovers from the port from Mathlib3. (They contain content moved from lean3 itself that Mathlib needed but was not moved to lean4.)

We intend to move all the content of these files out into the main Mathlib directory structure. Contributions assisting with this are appreciated.

multiplication

theorem Nat.eq_zero_of_mul_eq_zero {n : ℕ} {m : ℕ} : n * m = 0 → n = 0 ∨ m = 0

properties of inequality

def Nat.ltGeByCases {a : ℕ} {b : ℕ} {C : Sort u} (h₁ : a < b → C) (h₂ : b ≤ a → C) : C

Equations

• Nat.ltGeByCases h₁ h₂ = Decidable.byCases h₁ fun (h : ¬a < b) => h₂ ⋯

def Nat.ltByCases {a : ℕ} {b : ℕ} {C : Sort u} (h₁ : a < b → C) (h₂ : a = b → C) (h₃ : b < a → C) : C

Equations

• Nat.ltByCases h₁ h₂ h₃ = Nat.ltGeByCases h₁ fun (h₁ : b ≤ a) => Nat.ltGeByCases h₃ fun (h : a ≤ b) => h₂ ⋯

bit0/bit1 properties

successor and predecessor

def Nat.discriminate {B : Sort u} {n : ℕ} (H1 : n = 0 → B) (H2 : (m : ℕ) → n = m.succ → B) : B

Equations

• One or more equations did not get rendered due to their size.

theorem Nat.one_eq_succ_zero : 1 = Nat.succ 0

subtraction

Many lemmas are proven more generally in mathlib algebra/order/sub

min

induction principles

def Nat.twoStepInduction {P : ℕ → Sort u} (H1 : P 0) (H2 : P 1) (H3 : (n : ℕ) → P n → P n.succ → P n.succ.succ) (a : ℕ) : P a

Equations

• Nat.twoStepInduction H1 H2 H3 0 = H1
• Nat.twoStepInduction H1 H2 H3 1 = H2
• Nat.twoStepInduction H1 H2 H3 _n.succ.succ = H3 _n (Nat.twoStepInduction H1 H2 H3 _n) (Nat.twoStepInduction H1 H2 H3 _n.succ)

def Nat.subInduction {P : ℕ → ℕ → Sort u} (H1 : (m : ℕ) → P 0 m) (H2 : (n : ℕ) → P n.succ 0) (H3 : (n m : ℕ) → P n m → P n.succ m.succ) (n : ℕ) (m : ℕ) : P n m

Equations

• Nat.subInduction H1 H2 H3 0 x = H1 x
• Nat.subInduction H1 H2 H3 _n.succ 0 = H2 _n
• Nat.subInduction H1 H2 H3 n.succ m.succ = H3 n m (Nat.subInduction H1 H2 H3 n m)

theorem Nat.strong_induction_on {p : ℕ → Prop} (n : ℕ) (h : ∀ (n : ℕ), (∀ (m : ℕ), m < n → p m) → p n) : p n

theorem Nat.case_strong_induction_on {p : ℕ → Prop} (a : ℕ) (hz : p 0) (hi : ∀ (n : ℕ), (∀ (m : ℕ), m ≤ n → p m) → p n.succ) : p a

mod

theorem Nat.cond_decide_mod_two (x : ℕ) [d : Decidable (x % 2 = 1)] : (bif decide (x % 2 = 1) then 1 else 0) = x % 2

div

dvd