Theorem: ArithmeticFunction.IsMultiplicative.lcm_apply_mul_gcd_apply
File: Mathlib/NumberTheory/ArithmeticFunction.lean

Proof steps:
state_before: R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case pos
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : x = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y

case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
tactic: by_cases hx : x = 0
state_before: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case pos
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : y = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y

case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
tactic: by_cases hy : y = 0
state_before: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
tactic: have hgcd_ne_zero : x.gcd y ≠ 0 := gcd_ne_zero_left hx
state_before: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
tactic: have hlcm_ne_zero : x.lcm y ≠ 0 := lcm_ne_zero hx hy
state_before: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
tactic: have hfi_zero : ∀ {i}, f (i ^ 0) = 1 := by
    intro i; rw [Nat.pow_zero, hf.1]
state_before: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ f (x.lcm y) * f (x.gcd y) = f x * f y
state_after: case neg
R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ (∏ x_1 ∈ x.primeFactors ⊔ y.primeFactors, f (x_1 ^ (x.lcm y).factorization x_1)) *
      ∏ x_1 ∈ x.primeFactors ⊔ y.primeFactors, f (x_1 ^ (x.gcd y).factorization x_1) =
    (∏ x_1 ∈ x.primeFactors ⊔ y.primeFactors, f (x_1 ^ x.factorization x_1)) *
      ∏ x ∈ x.primeFactors ⊔ y.primeFactors, f (x ^ y.factorization x)

R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ y.factorization.support ⊆ x.primeFactors ⊔ y.primeFactors

R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ x.factorization.support ⊆ x.primeFactors ⊔ y.primeFactors

R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ (x.gcd y).factorization.support ⊆ x.primeFactors ⊔ y.primeFactors

R : Type u_1
inst✝ : CommMonoidWithZero R
f : ArithmeticFunction R
hf : f.IsMultiplicative
x y : ℕ
hx : ¬x = 0
hy : ¬y = 0
hgcd_ne_zero : x.gcd y ≠ 0
hlcm_ne_zero : x.lcm y ≠ 0
hfi_zero : ∀ {i : ℕ}, f (i ^ 0) = 1
⊢ (x.lcm y).factorization.support ⊆ x.primeFactors ⊔ y.primeFactors
tactic: iterate 4 rw [hf.multiplicative_factorization f (by assumption),
    Finsupp.prod_of_support_subset _ _ _ (fun _ _ => hfi_zero)
      (s := (x.primeFactors ⊔ y.primeFactors))]