intro m hm_pos hm
l : ℕ
⊢ ∀ n > 0,
    n ∈ {n | Squarefree n} →
      (∑ x ∈ n.divisorsAntidiagonal, μ x.1 • if l = x.2 then μ l else 0) = if l ∣ n then μ n 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