conv => { lhs; congr; rw [←Nat.prod_primeFactors_of_squarefree hd] }
M : ℕ
f : ArithmeticFunction ℝ
hf : CompletelyMultiplicative f
hf_nonneg : ∀ (n : ℕ), 0 ≤ f n
d : ℕ
hd : Squarefree d
hf_size : ∀ (n : ℕ), n.Prime → n ∣ d → f n < 1
⊢ f d * ∏ p ∈ d.primeFactors, 1 / (1 - f p) = ∏ p ∈ d.primeFactors, f p / (1 - f p)
M : ℕ
f : ArithmeticFunction ℝ
hf : CompletelyMultiplicative f
hf_nonneg : ∀ (n : ℕ), 0 ≤ f n
d : ℕ
hd : Squarefree d
hf_size : ∀ (n : ℕ), n.Prime → n ∣ d → f n < 1
⊢ f (∏ p ∈ d.primeFactors, p) * ∏ p ∈ d.primeFactors, 1 / (1 - f p) = ∏ p ∈ d.primeFactors, f p / (1 - f p)