-- Mathlib/MeasureTheory/Measure/Haar/Quotient.lean
theorem IsFundamentalDomain.QuotientMeasureEqMeasurePreimage_smulHaarMeasure {𝓕 : Set G}
    (h𝓕 : IsFundamentalDomain Γ.op 𝓕 ν) (h𝓕_finite : ν 𝓕 ≠ ⊤) :
    QuotientMeasureEqMeasurePreimage ν
      ((ν ((π ⁻¹' (K : Set (G ⧸ Γ))) ∩ 𝓕)) • haarMeasure K)

Proof state:
case neTopV
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ μ ↑K ≠ ⊤

Tactic:
rw [hμK]

Result:
case neTopV
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ c ≠ ⊤

Proof state:
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ QuotientMeasureEqMeasurePreimage ν μ

Tactic:
apply IsFundamentalDomain.QuotientMeasureEqMeasurePreimage_HaarMeasure (h𝓕 := h𝓕)
  (meas_V := K.isCompact.measurableSet) (μ := μ)

Result:
case hV
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ (interior ↑K).Nonempty

case hμK
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ μ ↑K = ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)

case neTopV
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
hμK : μ ↑K = c
this : SigmaFinite μ
⊢ μ ↑K ≠ ⊤

Proof state:
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
h𝓕_finite : c = ⊤
this : ⊤ ≤ ν 𝓕
⊢ ν 𝓕 = ⊤

Tactic:
exact top_unique this

Result:
no goals

Proof state:
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
c_ne_top : c ≠ ⊤
μ : Measure (G ⧸ Γ) := c • haarMeasure K
⊢ μ ↑K = c

Tactic:
simp [μ, haarMeasure_self]

Result:
no goals

Proof state:
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
h𝓕_finite : c = ⊤
⊢ ν 𝓕 = ⊤

Tactic:
have : c ≤ ν 𝓕 := measure_mono (Set.inter_subset_right)

Result:
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
c : ℝ≥0∞ := ν (QuotientGroup.mk ⁻¹' ↑K ∩ 𝓕)
h𝓕_finite : c = ⊤
this : c ≤ ν 𝓕
⊢ ν 𝓕 = ⊤

Proof state:
case intro
G : Type u_1
inst✝¹² : Group G
inst✝¹¹ : MeasurableSpace G
inst✝¹⁰ : TopologicalSpace G
inst✝⁹ : IsTopologicalGroup G
inst✝⁸ : BorelSpace G
inst✝⁷ : PolishSpace G
Γ : Subgroup G
inst✝⁶ : Γ.Normal
inst✝⁵ : T2Space (G ⧸ Γ)
inst✝⁴ : SecondCountableTopology (G ⧸ Γ)
inst✝³ : Countable ↥Γ
ν : Measure G
inst✝² : ν.IsHaarMeasure
inst✝¹ : ν.IsMulRightInvariant
inst✝ : SigmaFinite ν
K : PositiveCompacts (G ⧸ Γ)
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 ν
h𝓕_finite : ν 𝓕 ≠ ⊤
c : ℝ≥0
μ : Measure (G ⧸ Γ) := ↑c • haarMeasure K
hμK : μ ↑K = ↑c
⊢ SigmaFinite μ

Tactic:
exact SMul.sigmaFinite c

Result:
no goals