Theorem: MeasureTheory.Martingale.stoppedValue_ae_eq_condexp_of_le_const_of_countable_range
File: Mathlib/Probability/Martingale/OptionalSampling.lean

Proof steps:
state_before: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
⊢ stoppedValue f τ =ᶠ[ae μ] μ[f n|hτ.measurableSpace]
state_after: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ stoppedValue f τ =ᶠ[ae μ] μ[f n|hτ.measurableSpace]
tactic: have : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i} := by
    ext1 x
    simp only [Set.mem_univ, Set.mem_range, true_and_iff, Set.iUnion_exists, Set.iUnion_iUnion_eq',
      Set.mem_iUnion, Set.mem_setOf_eq, exists_apply_eq_apply']
state_before: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ stoppedValue f τ =ᶠ[ae μ] μ[f n|hτ.measurableSpace]
state_after: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ stoppedValue f τ =ᶠ[ae (μ.restrict Set.univ)] μ[f n|hτ.measurableSpace]
tactic: nth_rw 1 [← @Measure.restrict_univ Ω _ μ]
state_before: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ stoppedValue f τ =ᶠ[ae (μ.restrict Set.univ)] μ[f n|hτ.measurableSpace]
state_after: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ ∀ i ∈ Set.range τ, stoppedValue f τ =ᶠ[ae (μ.restrict {x | τ x = i})] μ[f n|hτ.measurableSpace]
tactic: rw [this, ae_eq_restrict_biUnion_iff _ h_countable_range]
state_before: Ω : Type u_1
E : Type u_2
m : MeasurableSpace Ω
μ : Measure Ω
inst✝⁸ : NormedAddCommGroup E
inst✝⁷ : NormedSpace ℝ E
inst✝⁶ : CompleteSpace E
ι : Type u_3
inst✝⁵ : LinearOrder ι
inst✝⁴ : TopologicalSpace ι
inst✝³ : OrderTopology ι
inst✝² : FirstCountableTopology ι
ℱ : Filtration ι m
inst✝¹ : SigmaFiniteFiltration μ ℱ
τ σ : Ω → ι
f : ι → Ω → E
i n : ι
h : Martingale f ℱ μ
hτ : IsStoppingTime ℱ τ
hτ_le : ∀ (x : Ω), τ x ≤ n
h_countable_range : (Set.range τ).Countable
inst✝ : SigmaFinite (μ.trim ⋯)
this : Set.univ = ⋃ i ∈ Set.range τ, {x | τ x = i}
⊢ ∀ i ∈ Set.range τ, stoppedValue f τ =ᶠ[ae (μ.restrict {x | τ x = i})] μ[f n|hτ.measurableSpace]
state_after: no goals
tactic: exact fun i _ => stoppedValue_ae_eq_restrict_eq h _ hτ_le i