Theorem: MeasureTheory.StronglyMeasurable.finStronglyMeasurable_of_set_sigmaFinite
File: Mathlib/MeasureTheory/Function/StronglyMeasurable/Basic.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ : SigmaFinite (μ.restrict t)
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
⊢ FinStronglyMeasurable f μ
tactic: haveI : SigmaFinite (μ.restrict t) := htμ
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
⊢ FinStronglyMeasurable f μ
tactic: let S := spanningSets (μ.restrict t)
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
⊢ FinStronglyMeasurable f μ
tactic: have hS_meas : ∀ n, MeasurableSet (S n) := measurable_spanningSets (μ.restrict t)
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
⊢ FinStronglyMeasurable f μ
tactic: let f_approx := hf_meas.approx
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
⊢ FinStronglyMeasurable f μ
tactic: let fs n := SimpleFunc.restrict (f_approx n) (S n ∩ t)
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
⊢ FinStronglyMeasurable f μ
state_after: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
h_fs_t_compl : ∀ (n : ℕ), ∀ x ∉ t, ↑(fs n) x = 0
⊢ FinStronglyMeasurable f μ
tactic: have h_fs_t_compl : ∀ n, ∀ x, x ∉ t → fs n x = 0 := by
    intro n x hxt
    rw [SimpleFunc.restrict_apply _ ((hS_meas n).inter ht)]
    refine Set.indicator_of_not_mem ?_ _
    simp [hxt]
state_before: α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
h_fs_t_compl : ∀ (n : ℕ), ∀ x ∉ t, ↑(fs n) x = 0
⊢ FinStronglyMeasurable f μ
state_after: case refine_1
α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
h_fs_t_compl : ∀ (n : ℕ), ∀ x ∉ t, ↑(fs n) x = 0
⊢ ∀ (n : ℕ), μ (support ↑(fs n)) < ⊤

case refine_2
α : Type u_1
β : Type u_2
γ : Type u_3
ι : Type u_4
inst✝² : Countable ι
f g : α → β
inst✝¹ : TopologicalSpace β
inst✝ : Zero β
m : MeasurableSpace α
μ : Measure α
hf_meas : StronglyMeasurable f
t : Set α
ht : MeasurableSet t
hft_zero : ∀ x ∈ tᶜ, f x = 0
htμ this : SigmaFinite (μ.restrict t)
S : ℕ → Set α := spanningSets (μ.restrict t)
hS_meas : ∀ (n : ℕ), MeasurableSet (S n)
f_approx : ℕ → α →ₛ β := hf_meas.approx
fs : ℕ → α →ₛ β := fun n => (f_approx n).restrict (S n ∩ t)
h_fs_t_compl : ∀ (n : ℕ), ∀ x ∉ t, ↑(fs n) x = 0
x : α
⊢ Tendsto (fun n => ↑(fs n) x) atTop (𝓝 (f x))
tactic: refine ⟨fs, ?_, fun x => ?_⟩