-- Mathlib/MeasureTheory/Measure/Haar/Unique.lean
theorem measure_isHaarMeasure_eq_smul_of_isEverywherePos [LocallyCompactSpace G]
    (μ' μ : Measure G) [IsHaarMeasure μ] [IsHaarMeasure μ']
    {s : Set G} (hs : MeasurableSet s) (h's : IsEverywherePos μ s) :
    μ' s = haarScalarFactor μ' μ • μ s

Proof state:
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
m : Set G
m_max : Maximal (fun x => x ∈ A) m
hms : m ⊆ s
hdj : m.PairwiseDisjoint fun x => x • k
sm : s ⊆ ⋃ x ∈ m, x • (k * k⁻¹)
hm : m.Nonempty
ρ : Measure G
hρ : ρ.IsEverywherePos s
M : ∀ (i : ↑m), MeasurableSet (s ∩ ↑i • k)
h'm : ρ s ≠ ⊤
this✝¹ : ∑' (x : ↑m), ρ (s ∩ ↑x • k) < ⊤
C : univ.Countable
this✝ : (support fun i => ρ (s ∩ ↑i • k)) = univ
this : Countable ↑m
⊢ m.Countable

Tactic:
exact to_countable m

Result:
no goals

Proof state:
case intro.intro.intro.intro.intro.inl
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
m_max : Maximal (fun x => x ∈ A) ∅
hms : ∅ ⊆ s
hdj : ∅.PairwiseDisjoint fun x => x • k
sm : s ⊆ ⋃ x ∈ ∅, x • (k * k⁻¹)
⊢ μ' s = ν s

Tactic:
simp only [mem_empty_iff_false, iUnion_of_empty, iUnion_empty, subset_empty_iff] at sm

Result:
case intro.intro.intro.intro.intro.inl
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
m_max : Maximal (fun x => x ∈ A) ∅
hms : ∅ ⊆ s
hdj : ∅.PairwiseDisjoint fun x => x • k
sm : s = ∅
⊢ μ' s = ν s

Proof state:
case pos.intro
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
f : ℕ → G
m_max : Maximal (fun x => x ∈ A) (range f)
hms : range f ⊆ s
hdj : (range f).PairwiseDisjoint fun x => x • k
sm : s ⊆ ⋃ x ∈ range f, x • (k * k⁻¹)
hm : (range f).Nonempty
h'm : (range f).Countable
M : ∀ (i : ℕ), MeasurableSet (disjointed (fun n => s ∩ f n • (k * k⁻¹)) i)
⊢ μ' s = ν s

Tactic:
simp only [mem_range, iUnion_exists, iUnion_iUnion_eq'] at sm

Result:
case pos.intro
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
f : ℕ → G
m_max : Maximal (fun x => x ∈ A) (range f)
hms : range f ⊆ s
hdj : (range f).PairwiseDisjoint fun x => x • k
hm : (range f).Nonempty
h'm : (range f).Countable
M : ∀ (i : ℕ), MeasurableSet (disjointed (fun n => s ∩ f n • (k * k⁻¹)) i)
sm : s ⊆ ⋃ y, f y • (k * k⁻¹)
⊢ μ' s = ν s

Proof state:
case pos.intro
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
f : ℕ → G
m_max : Maximal (fun x => x ∈ A) (range f)
hms : range f ⊆ s
hdj : (range f).PairwiseDisjoint fun x => x • k
hm : (range f).Nonempty
h'm : (range f).Countable
M : ∀ (i : ℕ), MeasurableSet (disjointed (fun n => s ∩ f n • (k * k⁻¹)) i)
sm : s ⊆ ⋃ y, f y • (k * k⁻¹)
⊢ μ' s = ν s

Tactic:
have s_eq : s = ⋃ n, s ∩ (f n • (k * k⁻¹)) := by rwa [← inter_iUnion, eq_comm, inter_eq_left]

Result:
case pos.intro
G : Type u_1
inst✝⁷ : TopologicalSpace G
inst✝⁶ : Group G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : MeasurableSpace G
inst✝³ : BorelSpace G
inst✝² : LocallyCompactSpace G
μ' μ : Measure G
inst✝¹ : μ.IsHaarMeasure
inst✝ : μ'.IsHaarMeasure
s : Set G
hs : MeasurableSet s
h's : μ.IsEverywherePos s
ν : Measure G := μ'.haarScalarFactor μ • μ
k : Set G
k_comp : IsCompact k
k_closed : IsClosed k
k_mem : k ∈ 𝓝 1
one_k : 1 ∈ k
A : Set (Set G) := {t | t ⊆ s ∧ t.PairwiseDisjoint fun x => x • k}
f : ℕ → G
m_max : Maximal (fun x => x ∈ A) (range f)
hms : range f ⊆ s
hdj : (range f).PairwiseDisjoint fun x => x • k
hm : (range f).Nonempty
h'm : (range f).Countable
M : ∀ (i : ℕ), MeasurableSet (disjointed (fun n => s ∩ f n • (k * k⁻¹)) i)
sm : s ⊆ ⋃ y, f y • (k * k⁻¹)
s_eq : s = ⋃ n, s ∩ f n • (k * k⁻¹)
⊢ μ' s = ν s