rw [h2, mul_one]
i : ℕ
hi : i < 330
h1 : ↑(1319 - i) = 1319 - ↑i
h2 : (660 + ↑i) * (1319 - ↑i) / ((660 + ↑i) * (1319 - ↑i)) = 1
⊢ (∏ x ∈ (Finset.range 330).erase i, (660 + ↑x) * ↑(1319 - x)) *
      ((660 + ↑i) * (1319 - ↑i) / ((660 + ↑i) * (1319 - ↑i))) =
    ∏ x ∈ (Finset.range 330).erase i, (660 + ↑x) * ↑(1319 - x)
no goals