-- Mathlib/MeasureTheory/Measure/Haar/Quotient.lean
/-- The `essSup` of a function `g` on the quotient space `G ⧸ Γ` with respect to the pushforward
  of the restriction, `μ_𝓕`, of a right-invariant measure `μ` to a fundamental domain `𝓕`, is the
  same as the `essSup` of `g`'s lift to the universal cover `G` with respect to `μ`. -/
@[to_additive "The `essSup` of a function `g` on the additive quotient space `G ⧸ Γ` with respect
  to the pushforward of the restriction, `μ_𝓕`, of a right-invariant measure `μ` to a fundamental
  domain `𝓕`, is the same as the `essSup` of `g`'s lift to the universal cover `G` with respect
  to `μ`."]
lemma essSup_comp_quotientGroup_mk [μ.IsMulRightInvariant] {g : G ⧸ Γ → ℝ≥0∞}
    (g_ae_measurable : AEMeasurable g μ_𝓕) : essSup g μ_𝓕 = essSup (fun (x : G) ↦ g x) μ

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
⊢ essSup g (map QuotientGroup.mk (μ.restrict 𝓕)) = essSup (fun x => g ↑x) μ

Tactic:
have hπ : Measurable (QuotientGroup.mk : G → G ⧸ Γ) := continuous_quotient_mk'.measurable

Result:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ essSup g (map QuotientGroup.mk (μ.restrict 𝓕)) = essSup (fun x => g ↑x) μ

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ essSup (g ∘ QuotientGroup.mk) (μ.restrict 𝓕) = essSup (fun x => g ↑x) μ

Tactic:
refine h𝓕.essSup_measure_restrict ?_

Result:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ ∀ (γ : ↥Γ.op) (x : G), (g ∘ QuotientGroup.mk) (γ • x) = (g ∘ QuotientGroup.mk) x

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ essSup g (map QuotientGroup.mk (μ.restrict 𝓕)) = essSup (fun x => g ↑x) μ

Tactic:
rw [essSup_map_measure g_ae_measurable hπ.aemeasurable]

Result:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ essSup (g ∘ QuotientGroup.mk) (μ.restrict 𝓕) = essSup (fun x => g ↑x) μ

Proof state:
case e_a
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
γ : Gᵐᵒᵖ
hγ : γ ∈ Γ.op
x : G
⊢ ↑(x * MulOpposite.unop γ) = ↑x

Tactic:
exact QuotientGroup.mk_mul_of_mem x hγ

Result:
no goals

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
⊢ ∀ (γ : ↥Γ.op) (x : G), (g ∘ QuotientGroup.mk) (γ • x) = (g ∘ QuotientGroup.mk) x

Tactic:
intro ⟨γ, hγ⟩ x

Result:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
γ : Gᵐᵒᵖ
hγ : γ ∈ Γ.op
x : G
⊢ (g ∘ QuotientGroup.mk) (⟨γ, hγ⟩ • x) = (g ∘ QuotientGroup.mk) x

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
γ : Gᵐᵒᵖ
hγ : γ ∈ Γ.op
x : G
⊢ g ↑(x * MulOpposite.unop γ) = g ↑x

Tactic:
congr 1

Result:
case e_a
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : IsTopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥Γ.op) 𝓕 μ
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : μ.IsMulRightInvariant
g : G ⧸ Γ → ℝ≥0∞
g_ae_measurable : AEMeasurable g (map QuotientGroup.mk (μ.restrict 𝓕))
hπ : Measurable QuotientGroup.mk
γ : Gᵐᵒᵖ
hγ : γ ∈ Γ.op
x : G
⊢ ↑(x * MulOpposite.unop γ) = ↑x