apply sum_congr rfl
case a
s : Sieve
l : ℕ
hl : Squarefree l
hnu_nonzero : ν l ≠ 0
⊢ ∑ i ∈ l.divisors, ↑(μ i) * (ν (l / i))⁻¹ = ∑ i ∈ l.divisors, (ν l)⁻¹ * (↑(μ i) * ν i)
case a
s : Sieve
l : ℕ
hl : Squarefree l
hnu_nonzero : ν l ≠ 0
⊢ ∀ x ∈ l.divisors, ↑(μ x) * (ν (l / x))⁻¹ = (ν l)⁻¹ * (↑(μ x) * ν x)