Theorem: measurableSet_tendsto
File: Mathlib/MeasureTheory/MeasurableSpace/Basic.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
⊢ MeasurableSet {x | Tendsto (fun n => f n x) l l'}
state_after: case intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
⊢ MeasurableSet {x | Tendsto (fun n => f n x) l l'}
tactic: rcases l.exists_antitone_basis with ⟨u, hu⟩
state_before: case intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
⊢ MeasurableSet {x | Tendsto (fun n => f n x) l l'}
state_after: case intro.intro.intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
v : ℕ → Set γ
v_meas : ∀ (i : ℕ), v i ∈ l' ∧ MeasurableSet (v i)
hv : l'.HasAntitoneBasis fun i => id (v i)
⊢ MeasurableSet {x | Tendsto (fun n => f n x) l l'}
tactic: rcases (Filter.hasBasis_self.mpr hl'.exists_measurable_subset).exists_antitone_subbasis with
    ⟨v, v_meas, hv⟩
state_before: case intro.intro.intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
v : ℕ → Set γ
v_meas : ∀ (i : ℕ), v i ∈ l' ∧ MeasurableSet (v i)
hv : l'.HasAntitoneBasis fun i => id (v i)
⊢ MeasurableSet {x | Tendsto (fun n => f n x) l l'}
state_after: case intro.intro.intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
v : ℕ → Set γ
v_meas : ∀ (i : ℕ), v i ∈ l' ∧ MeasurableSet (v i)
hv : l'.HasAntitoneBasis fun i => id (v i)
⊢ MeasurableSet (⋂ i, ⋃ i_1, ⋂ i_2 ∈ u i_1, {x | f i_2 x ∈ id (v i)})
tactic: simp only [hu.tendsto_iff hv.toHasBasis, true_imp_iff, true_and, setOf_forall, setOf_exists]
state_before: case intro.intro.intro
α : Type u_1
β : Type u_2
γ : Type u_3
δ : Type u_4
δ' : Type u_5
ι : Sort uι
s t u✝ : Set α
x✝ : MeasurableSpace β
inst✝³ : MeasurableSpace γ
inst✝² : Countable δ
l : Filter δ
inst✝¹ : l.IsCountablyGenerated
l' : Filter γ
inst✝ : l'.IsCountablyGenerated
hl' : l'.IsMeasurablyGenerated
f : δ → β → γ
hf : ∀ (i : δ), Measurable (f i)
u : ℕ → Set δ
hu : l.HasAntitoneBasis u
v : ℕ → Set γ
v_meas : ∀ (i : ℕ), v i ∈ l' ∧ MeasurableSet (v i)
hv : l'.HasAntitoneBasis fun i => id (v i)
⊢ MeasurableSet (⋂ i, ⋃ i_1, ⋂ i_2 ∈ u i_1, {x | f i_2 x ∈ id (v i)})
state_after: no goals
tactic: exact .iInter fun n ↦ .iUnion fun _ ↦ .biInter (to_countable _) fun i _ ↦
    (v_meas n).2.preimage (hf i)