l3lab/ntp-mathlib huggingface dataset:
/-- 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 := by
  have hπ : Measurable (QuotientGroup.mk : G → G ⧸ Γ) := continuous_quotient_mk'.measurable
  rw [essSup_map_measure g_ae_measurable hπ.aemeasurable]
  refine h𝓕.essSup_measure_restrict ?_
  intro ⟨γ, hγ⟩ x
  dsimp
  congr 1
  

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

Next tactic:
exact QuotientGroup.mk_mul_of_mem x hγ
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
⊢ map QuotientGroup.mk μ ≪ map QuotientGroup.mk (Measure.restrict μ 𝓕)

Next tactic:
set π : G → G ⧸ Γ := QuotientGroup.mk
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
⊢ map π μ ≪ map π (Measure.restrict μ 𝓕)

Next tactic:
have meas_π : Measurable π := continuous_quotient_mk'.measurable
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
⊢ map π μ ≪ map π (Measure.restrict μ 𝓕)

Next tactic:
apply AbsolutelyContinuous.mk
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
⊢ ∀ ⦃s : Set (G ⧸ Γ)⦄, MeasurableSet s → ↑↑(map π (Measure.restrict μ 𝓕)) s = 0 → ↑↑(map π μ) s = 0

Next tactic:
intro s s_meas hs
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑(map π (Measure.restrict μ 𝓕)) s = 0
⊢ ↑↑(map π μ) s = 0

Next tactic:
rw [map_apply meas_π s_meas] at hs ⊢
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑(Measure.restrict μ 𝓕) (π ⁻¹' s) = 0
⊢ ↑↑μ (π ⁻¹' s) = 0

Next tactic:
rw [Measure.restrict_apply] at hs
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
⊢ ↑↑μ (π ⁻¹' s) = 0
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑(Measure.restrict μ 𝓕) (π ⁻¹' s) = 0
⊢ MeasurableSet (π ⁻¹' s)

Next tactic:
apply h𝓕.measure_zero_of_invariant _ _ hs
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  apply h𝓕.measure_zero_of_invariant _ _ hs
  · 

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
⊢ ∀ (g : ↥(Subgroup.op Γ)), g • π ⁻¹' s = π ⁻¹' s

Next tactic:
intro γ
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  apply h𝓕.measure_zero_of_invariant _ _ hs
  · intro γ
    

Proof state:
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
γ : ↥(Subgroup.op Γ)
⊢ γ • π ⁻¹' s = π ⁻¹' s

Next tactic:
ext g
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  apply h𝓕.measure_zero_of_invariant _ _ hs
  · intro γ
    ext g
    

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
γ : ↥(Subgroup.op Γ)
g : G
⊢ g ∈ γ • π ⁻¹' s ↔ g ∈ π ⁻¹' s

Next tactic:
rw [Set.mem_smul_set_iff_inv_smul_mem, mem_preimage, mem_preimage]
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  apply h𝓕.measure_zero_of_invariant _ _ hs
  · intro γ
    ext g
    rw [Set.mem_smul_set_iff_inv_smul_mem, mem_preimage, mem_preimage]
    

Proof state:
case h
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
γ : ↥(Subgroup.op Γ)
g : G
⊢ π (γ⁻¹ • g) ∈ s ↔ π g ∈ s

Next tactic:
congr! 1
/-- Given a quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the restriction,
  `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient! -/
@[to_additive "Given an additive quotient space `G ⧸ Γ` where `Γ` is `Countable`, and the
  restriction, `μ_𝓕`, of a right-invariant measure `μ` on `G` to a fundamental domain `𝓕`, a set
  in the quotient which has `μ_𝓕`-measure zero, also has measure zero under the
  folding of `μ` under the quotient. Note that, if `Γ` is infinite, then the folded map
  will take the value `∞` on any open set in the quotient!"]
lemma _root_.MeasureTheory.IsFundamentalDomain.absolutelyContinuous_map
    [μ.IsMulRightInvariant] :
    map (QuotientGroup.mk : G → G ⧸ Γ) μ ≪ map (QuotientGroup.mk : G → G ⧸ Γ) (μ.restrict 𝓕) := by
  set π : G → G ⧸ Γ := QuotientGroup.mk
  have meas_π : Measurable π := continuous_quotient_mk'.measurable
  apply AbsolutelyContinuous.mk
  intro s s_meas hs
  rw [map_apply meas_π s_meas] at hs ⊢
  rw [Measure.restrict_apply] at hs
  apply h𝓕.measure_zero_of_invariant _ _ hs
  · intro γ
    ext g
    rw [Set.mem_smul_set_iff_inv_smul_mem, mem_preimage, mem_preimage]
    congr! 1
    

Proof state:
case h.a.h.e'_4
G : Type u_1
inst✝⁸ : Group G
inst✝⁷ : MeasurableSpace G
inst✝⁶ : TopologicalSpace G
inst✝⁵ : TopologicalGroup G
inst✝⁴ : BorelSpace G
μ : Measure G
Γ : Subgroup G
𝓕 : Set G
h𝓕 : IsFundamentalDomain (↥(Subgroup.op Γ)) 𝓕
inst✝³ : Countable ↥Γ
inst✝² : MeasurableSpace (G ⧸ Γ)
inst✝¹ : BorelSpace (G ⧸ Γ)
inst✝ : IsMulRightInvariant μ
π : G → G ⧸ Γ := QuotientGroup.mk
meas_π : Measurable π
s : Set (G ⧸ Γ)
s_meas : MeasurableSet s
hs : ↑↑μ (π ⁻¹' s ∩ 𝓕) = 0
γ : ↥(Subgroup.op Γ)
g : G
⊢ π (γ⁻¹ • g) = π g

Next tactic:
convert QuotientGroup.mk_mul_of_mem g (γ⁻¹).2 using 1