-- Mathlib/MeasureTheory/Integral/DominatedConvergence.lean
theorem hasSum_integral_of_dominated_convergence {ι} [Countable ι] {F : ι → α → G} {f : α → G}
    (bound : ι → α → ℝ) (hF_meas : ∀ n, AEStronglyMeasurable (F n) μ)
    (h_bound : ∀ n, ∀ᵐ a ∂μ, ‖F n a‖ ≤ bound n a)
    (bound_summable : ∀ᵐ a ∂μ, Summable fun n => bound n a)
    (bound_integrable : Integrable (fun a => ∑' n, bound n a) μ)
    (h_lim : ∀ᵐ a ∂μ, HasSum (fun n => F n a) (f a)) :
    HasSum (fun n => ∫ a, F n a ∂μ) (∫ a, f a ∂μ)

Proof state:
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
hb_le_tsum : ∀ (n : ι), bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a
⊢ HasSum (fun n => ∫ (a : α), F n a ∂μ) (∫ (a : α), f a ∂μ)

Tactic:
have hF_integrable : ∀ n, Integrable (F n) μ := by
  refine fun n => bound_integrable.mono' (hF_meas n) ?_
  exact EventuallyLE.trans (h_bound n) (hb_le_tsum n)

Result:
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
hb_le_tsum : ∀ (n : ι), bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a
hF_integrable : ∀ (n : ι), Integrable (F n) μ
⊢ HasSum (fun n => ∫ (a : α), F n a ∂μ) (∫ (a : α), f a ∂μ)

Proof state:
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
hb_le_tsum : ∀ (n : ι), bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a
⊢ ∀ (n : ι), Integrable (F n) μ

Tactic:
refine fun n => bound_integrable.mono' (hF_meas n) ?_

Result:
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
hb_le_tsum : ∀ (n : ι), bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a
n : ι
⊢ ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ ∑' (n : ι), bound n a

Proof state:
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
n : ι
⊢ bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a

Tactic:
filter_upwards [hb_nonneg, bound_summable]
  with _ ha0 ha_sum using le_tsum ha_sum _ fun i _ => ha0 i

Result:
no goals

Proof state:
case h
α : Type u_1
G : Type u_3
inst✝² : NormedAddCommGroup G
inst✝¹ : NormedSpace ℝ G
m : MeasurableSpace α
μ : Measure α
ι : Type u_4
inst✝ : Countable ι
F : ι → α → G
f : α → G
bound : ι → α → ℝ
hF_meas : ∀ (n : ι), AEStronglyMeasurable (F n) μ
h_bound : ∀ (n : ι), ∀ᵐ (a : α) ∂μ, ‖F n a‖ ≤ bound n a
bound_summable : ∀ᵐ (a : α) ∂μ, Summable fun n => bound n a
bound_integrable : Integrable (fun a => ∑' (n : ι), bound n a) μ
h_lim : ∀ᵐ (a : α) ∂μ, HasSum (fun n => F n a) (f a)
hb_nonneg : ∀ᵐ (a : α) ∂μ, ∀ (n : ι), 0 ≤ bound n a
hb_le_tsum : ∀ (n : ι), bound n ≤ᶠ[ae μ] fun a => ∑' (n : ι), bound n a
hF_integrable : ∀ (n : ι), Integrable (F n) μ
s : Finset ι
a : α
hFa : ∀ (i : ι), ‖F i a‖ ≤ bound i a
ha0 : ∀ (n : ι), 0 ≤ bound n a
has : Summable fun n => bound n a
⊢ ‖∑ i ∈ s, F i a‖ ≤ ∑' (n : ι), bound n a

Tactic:
calc
  ‖∑ n ∈ s, F n a‖ ≤ ∑ n ∈ s, bound n a := norm_sum_le_of_le _ fun n _ => hFa n
  _ ≤ ∑' n, bound n a := sum_le_tsum _ (fun n _ => ha0 n) has

Result:
no goals