-- Mathlib/MeasureTheory/Measure/Haar/Unique.lean
/-- The parameterized integral `x ↦ ∫ y, g (y⁻¹ * x) ∂μ` depends continuously on `y` when `g` is a
compactly supported continuous function on a topological group `G`, and `μ` is finite on compact
sets. -/
@[to_additive]
lemma continuous_integral_apply_inv_mul
    {G : Type*} [TopologicalSpace G] [LocallyCompactSpace G] [Group G] [IsTopologicalGroup G]
    [MeasurableSpace G] [BorelSpace G]
    {μ : Measure G} [IsFiniteMeasureOnCompacts μ] {E : Type*} [NormedAddCommGroup E]
    [NormedSpace ℝ E] {g : G → E}
    (hg : Continuous g) (h'g : HasCompactSupport g) :
    Continuous (fun (x : G) ↦ ∫ y, g (y⁻¹ * x) ∂μ)

Proof state:
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
⊢ ContinuousOn (fun x => ∫ (y : G), g (y⁻¹ * x) ∂μ) t

Tactic:
apply continuousOn_integral_of_compact_support k'_comp

Result:
case hf
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
⊢ ContinuousOn (uncurry fun x y => g (y⁻¹ * x)) (t ×ˢ univ)

case hfs
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
⊢ ∀ (p x : G), p ∈ t → x ∉ k' → g (x⁻¹ * p) = 0

Proof state:
case hfs
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
⊢ ∀ (p x : G), p ∈ t → x ∉ k' → g (x⁻¹ * p) = 0

Tactic:
intro p x hp hx

Result:
case hfs
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
p x : G
hp : p ∈ t
hx : x ∉ k'
⊢ g (x⁻¹ * p) = 0

Proof state:
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
⊢ ContinuousAt (fun x => ∫ (y : G), g (y⁻¹ * x) ∂μ) x₀

Tactic:
obtain ⟨t, t_comp, ht⟩ : ∃ t, IsCompact t ∧ t ∈ 𝓝 x₀ := exists_compact_mem_nhds x₀

Result:
case intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
⊢ ContinuousAt (fun x => ∫ (y : G), g (y⁻¹ * x) ∂μ) x₀

Proof state:
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
p x : G
hp : p ∈ t
hx : g (x⁻¹ * p) ≠ 0
⊢ (fun x1 x2 => x1 • x2) p (p⁻¹ * x) = x

Tactic:
simp

Result:
no goals

Proof state:
case intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
⊢ ContinuousAt (fun x => ∫ (y : G), g (y⁻¹ * x) ∂μ) x₀

Tactic:
have k'_comp : IsCompact k' := t_comp.smul_set k_comp.inv

Result:
case intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
⊢ ContinuousAt (fun x => ∫ (y : G), g (y⁻¹ * x) ∂μ) x₀

Proof state:
case hfs
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
p x : G
hp : p ∈ t
hx : x ∉ k'
⊢ g (x⁻¹ * p) = 0

Tactic:
contrapose! hx

Result:
case hfs
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : LocallyCompactSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
μ : Measure G
inst✝² : IsFiniteMeasureOnCompacts μ
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : G → E
hg : Continuous g
h'g : HasCompactSupport g
k : Set G := tsupport g
k_comp : IsCompact k
x₀ : G
t : Set G
t_comp : IsCompact t
ht : t ∈ 𝓝 x₀
k' : Set G := t • k⁻¹
k'_comp : IsCompact k'
p x : G
hp : p ∈ t
hx : g (x⁻¹ * p) ≠ 0
⊢ x ∈ k'