-- Mathlib/MeasureTheory/Integral/DominatedConvergence.lean
theorem continuousAt_parametric_primitive_of_dominated [FirstCountableTopology X]
    {F : X → ℝ → E} (bound : ℝ → ℝ) (a b : ℝ)
    {a₀ b₀ : ℝ} {x₀ : X} (hF_meas : ∀ x, AEStronglyMeasurable (F x) (μ.restrict <| Ι a b))
    (h_bound : ∀ᶠ x in 𝓝 x₀, ∀ᵐ t ∂μ.restrict <| Ι a b, ‖F x t‖ ≤ bound t)
    (bound_integrable : IntervalIntegrable bound μ a b)
    (h_cont : ∀ᵐ t ∂μ.restrict <| Ι a b, ContinuousAt (fun x ↦ F x t) x₀) (ha₀ : a₀ ∈ Ioo a b)
    (hb₀ : b₀ ∈ Ioo a b) (hμb₀ : μ {b₀} = 0) :
    ContinuousAt (fun p : X × ℝ ↦ ∫ t : ℝ in a₀..p.2, F p.1 t ∂μ) (x₀, b₀)

Proof state:
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
⊢ Tendsto (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) (𝓝 b₀) (𝓝 0)

Tactic:
suffices ContinuousAt (fun t ↦ ∫ s in b₀..t, 2 * bound s ∂μ) b₀ by
  simpa [ContinuousAt] using this

Result:
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
⊢ ContinuousAt (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) b₀

Proof state:
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
⊢ ContinuousAt (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) b₀

Tactic:
apply ContinuousWithinAt.continuousAt _ Icc_nhds

Result:
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
⊢ ContinuousWithinAt (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) (Icc a b) b₀

Proof state:
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this✝ :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
this : ContinuousAt (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) b₀
⊢ Tendsto (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) (𝓝 b₀) (𝓝 0)

Tactic:
simpa [ContinuousAt] using this

Result:
no goals

Proof state:
case refine_3
E : Type u_1
X : Type u_2
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
inst✝¹ : TopologicalSpace X
μ : Measure ℝ
inst✝ : FirstCountableTopology X
F : X → ℝ → E
bound : ℝ → ℝ
a b a₀ b₀ : ℝ
x₀ : X
hF_meas : ∀ (x : X), AEStronglyMeasurable (F x) (μ.restrict (Ι a b))
h_bound : ∀ᶠ (x : X) in 𝓝 x₀, ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x t‖ ≤ bound t
bound_integrable : IntervalIntegrable bound μ a b
h_cont : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ContinuousAt (fun x => F x t) x₀
ha₀ : a₀ ∈ Ioo a b
hb₀ : b₀ ∈ Ioo a b
hμb₀ : μ {b₀} = 0
hsub : ∀ {a₀ b₀ : ℝ}, a₀ ∈ Ioo a b → b₀ ∈ Ioo a b → Ι a₀ b₀ ⊆ Ι a b
Ioo_nhds : Ioo a b ∈ 𝓝 b₀
Icc_nhds : Icc a b ∈ 𝓝 b₀
hx₀ : ∀ᵐ (t : ℝ) ∂μ.restrict (Ι a b), ‖F x₀ t‖ ≤ bound t
this✝ :
  ∀ᶠ (p : X × ℝ) in 𝓝 (x₀, b₀), ‖∫ (s : ℝ) in b₀..p.2, F p.1 s - F x₀ s ∂μ‖ ≤ |∫ (s : ℝ) in b₀..p.2, 2 * bound s ∂μ|
this : Tendsto (fun t => ∫ (s : ℝ) in b₀..t, 2 * bound s ∂μ) (𝓝 b₀) (𝓝 0)
⊢ Tendsto (fun n => |∫ (s : ℝ) in b₀..n.2, 2 * bound s ∂μ|) (𝓝 x₀ ×ˢ 𝓝 b₀) (𝓝 0)

Tactic:
exact (continuous_abs.tendsto' _ _ abs_zero).comp (this.comp tendsto_snd)

Result:
no goals