Theorem: MeasureTheory.QuotientMeasureEqMeasurePreimage.sigmaFiniteQuotient
File: Mathlib/MeasureTheory/Group/FundamentalDomain.lean

Proof steps:
state_before: G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
⊢ SigmaFinite μ
state_after: G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
tactic: rw [sigmaFinite_iff]
state_before: G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
state_after: case mk
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), A i ∈ {s | MeasurableSet s}
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
tactic: obtain ⟨A, hA_meas, hA, hA'⟩ := Measure.toFiniteSpanningSetsIn (h := i)
state_before: case mk
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), A i ∈ {s | MeasurableSet s}
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
state_after: case mk
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), MeasurableSet (A i)
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
tactic: simp only [mem_setOf_eq] at hA_meas
state_before: case mk
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), MeasurableSet (A i)
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
⊢ Nonempty (μ.FiniteSpanningSetsIn univ)
state_after: case mk.refine_1
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), MeasurableSet (A i)
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
n : ℕ
⊢ μ ((fun n => Quotient.mk α_mod_G '' A n) n) < ⊤

case mk.refine_2
G : Type u_1
H : Type u_2
α : Type u_3
β : Type u_4
E : Type u_5
inst✝⁷ : Group G
inst✝⁶ : MulAction G α
inst✝⁵ : MeasurableSpace α
ν : Measure α
inst✝⁴ : Countable G
inst✝³ : MeasurableSpace G
inst✝² : SMulInvariantMeasure G α ν
inst✝¹ : MeasurableSMul G α
i : SigmaFinite ν
i' : HasFundamentalDomain G α ν
μ : Measure (Quotient α_mod_G)
inst✝ : QuotientMeasureEqMeasurePreimage ν μ
A : ℕ → Set α
hA_meas : ∀ (i : ℕ), MeasurableSet (A i)
hA : ∀ (i : ℕ), ν (A i) < ⊤
hA' : ⋃ i, A i = univ
⊢ ⋃ i, (fun n => Quotient.mk α_mod_G '' A n) i = univ
tactic: refine ⟨⟨fun n ↦ π '' (A n), by simp, fun n ↦ ?_, ?_⟩⟩