rw [sum_divisorsAntidiagonal' (f:= fun x y => μ x • if l=y then μ l else 0)]
l m : ℕ
hm_pos : m > 0
hm : m ∈ {n | Squarefree n}
⊢ (∑ x ∈ m.divisorsAntidiagonal, μ x.1 • if l = x.2 then μ l else 0) = if l ∣ m then μ m else 0
l m : ℕ
hm_pos : m > 0
hm : m ∈ {n | Squarefree n}
⊢ (∑ i ∈ m.divisors, μ (m / i) • if l = i then μ l else 0) = if l ∣ m then μ m else 0