rw [← WithTop.add_right_cancel_iff hfin, ← ENat.tsum_add,
  tsum_congr (fun i ↦ tsub_add_cancel_of_le (h i)), tsub_add_cancel_of_le (ENat.tsum_le_tsum h)]
α : Type u_1
β : Type u_2
ι : Type u_3
s : Set α
n : ℕ∞
f g : α → ℕ∞
hfin : ∑' (a : α), g a ≠ ⊤
h : g ≤ f
⊢ ∑' (a : α), (f a - g a) = ∑' (a : α), f a - ∑' (a : α), g a
no goals