-- Mathlib/MeasureTheory/Integral/IntegralEqImproper.lean
theorem integrableOn_Ioi_of_intervalIntegral_norm_bounded (I a : ℝ)
    (hfi : ∀ i, IntegrableOn f (Ioc a (b i)) μ) (hb : Tendsto b l atTop)
    (h : ∀ᶠ i in l, (∫ x in a..b i, ‖f x‖ ∂μ) ≤ I) : IntegrableOn f (Ioi a) μ

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
⊢ IntegrableOn f (Ioi a) μ

Tactic:
have hfi : ∀ i, IntegrableOn f (Iic (b i)) (μ.restrict <| Ioi a) := by
  intro i
  rw [IntegrableOn, Measure.restrict_restrict (hφ.measurableSet i), inter_comm]
  exact hfi i

Result:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
⊢ IntegrableOn f (Ioi a) μ

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
⊢ ∀ᶠ (x : ι) in l, ∫ (x : ℝ) in a..b x, ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Iic (b x), ‖f x‖ ∂μ.restrict (Ioi a) ≤ I

Tactic:
filter_upwards [hb.eventually (eventually_ge_atTop a)] with i hbi

Result:
case h
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
i : ι
hbi : a ≤ b i
⊢ ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Iic (b i), ‖f x‖ ∂μ.restrict (Ioi a) ≤ I

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
i : ι
⊢ Integrable f (μ.restrict (Ioi a ∩ Iic (b i)))

Tactic:
exact hfi i

Result:
no goals

Proof state:
case h
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
i : ι
hbi : a ≤ b i
⊢ ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Iic (b i), ‖f x‖ ∂μ.restrict (Ioi a) ≤ I

Tactic:
rw [intervalIntegral.integral_of_le hbi, Measure.restrict_restrict (hφ.measurableSet i),
  inter_comm]

Result:
case h
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
i : ι
hbi : a ≤ b i
⊢ ∫ (x : ℝ) in Ioc a (b i), ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Ioi a ∩ Iic (b i), ‖f x‖ ∂μ ≤ I

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
⊢ ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))

Tactic:
intro i

Result:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
i : ι
⊢ IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
⊢ IntegrableOn f (Ioi a) μ

Tactic:
refine hφ.integrable_of_integral_norm_bounded I hfi (h.mp ?_)

Result:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
⊢ ∀ᶠ (x : ι) in l, ∫ (x : ℝ) in a..b x, ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Iic (b x), ‖f x‖ ∂μ.restrict (Ioi a) ≤ I

Proof state:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
⊢ IntegrableOn f (Ioi a) μ

Tactic:
have hφ : AECover (μ.restrict <| Ioi a) l _ := aecover_Iic hb

Result:
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
⊢ IntegrableOn f (Ioi a) μ

Proof state:
case h
ι : Type u_1
E : Type u_2
μ : Measure ℝ
l : Filter ι
inst✝² : l.NeBot
inst✝¹ : l.IsCountablyGenerated
inst✝ : NormedAddCommGroup E
b : ι → ℝ
f : ℝ → E
I a : ℝ
hfi✝ : ∀ (i : ι), IntegrableOn f (Ioc a (b i)) μ
hb : Tendsto b l atTop
h : ∀ᶠ (i : ι) in l, ∫ (x : ℝ) in a..b i, ‖f x‖ ∂μ ≤ I
hφ : AECover (μ.restrict (Ioi a)) l fun i => Iic (b i)
hfi : ∀ (i : ι), IntegrableOn f (Iic (b i)) (μ.restrict (Ioi a))
i : ι
hbi : a ≤ b i
⊢ ∫ (x : ℝ) in Ioc a (b i), ‖f x‖ ∂μ ≤ I → ∫ (x : ℝ) in Ioi a ∩ Iic (b i), ‖f x‖ ∂μ ≤ I

Tactic:
exact id

Result:
no goals