rw [tsum_congr (show ∀ (a : s), f a = (s.indicator f) a from _),
  tsum_congr ((show ∀ (a : ↑ (s ∩ f.support)), f a = (s.indicator f) a from _)),
  tsum_subtype_eq_of_support_subset (by simp), tsum_subtype_eq_of_support_subset (by simp)]
α✝ : Type u_1
β✝ : Type u_2
ι : Type u_3
s✝ : Set α✝
α : Type u_4
β : Type u_5
f : α → β
inst✝² : TopologicalSpace β
inst✝¹ : AddCommMonoid β
inst✝ : T2Space β
s : Set α
⊢ ∑' (x : ↑(s ∩ support f)), f ↑x = ∑' (x : ↑s), f ↑x
α✝ : Type u_1
β✝ : Type u_2
ι : Type u_3
s✝ : Set α✝
α : Type u_4
β : Type u_5
f : α → β
inst✝² : TopologicalSpace β
inst✝¹ : AddCommMonoid β
inst✝ : T2Space β
s : Set α
⊢ ∀ (a : ↑(s ∩ support f)), f ↑a = s.indicator f ↑a

α✝ : Type u_1
β✝ : Type u_2
ι : Type u_3
s✝ : Set α✝
α : Type u_4
β : Type u_5
f : α → β
inst✝² : TopologicalSpace β
inst✝¹ : AddCommMonoid β
inst✝ : T2Space β
s : Set α
⊢ ∀ (a : ↑s), f ↑a = s.indicator f ↑a