Theorem: MeasureTheory.Submartingale.sum_mul_upcrossingStrat_le
File: Mathlib/Probability/Martingale/Upcrossing.lean

Proof steps:
state_before: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
state_after: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ : 0 ≤ ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
tactic: have h₁ : (0 : ℝ) ≤
      μ[∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)] := by
    have := (hf.sum_sub_upcrossingStrat_mul a b N).setIntegral_le (zero_le n) MeasurableSet.univ
    rw [integral_univ, integral_univ] at this
    refine le_trans ?_ this
    simp only [Finset.range_zero, Finset.sum_empty, integral_zero', le_refl]
state_before: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ : 0 ≤ ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
state_after: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ : 0 ≤ ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
tactic: have h₂ : μ[∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)] =
    μ[∑ k ∈ Finset.range n, (f (k + 1) - f k)] -
      μ[∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)] := by
    simp only [sub_mul, one_mul, Finset.sum_sub_distrib, Pi.sub_apply, Finset.sum_apply,
      Pi.mul_apply]
    refine integral_sub (Integrable.sub (integrable_finset_sum _ fun i _ => hf.integrable _)
      (integrable_finset_sum _ fun i _ => hf.integrable _)) ?_
    convert (hf.sum_upcrossingStrat_mul a b N).integrable n using 1
    ext; simp
state_before: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ : 0 ≤ ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
state_after: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
tactic: rw [h₂, sub_nonneg] at h₁
state_before: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
state_after: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ ≤ ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
tactic: refine le_trans h₁ ?_
state_before: Ω : Type u_1
ι : Type u_2
m0 : MeasurableSpace Ω
μ : Measure Ω
a b : ℝ
f : ℕ → Ω → ℝ
N n m : ℕ
ω : Ω
ℱ : Filtration ℕ m0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
h₁ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ ≤
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ
h₂ :
  ∫ (x : Ω), (∑ k ∈ Finset.range n, (1 - upcrossingStrat a b f N k) * (f (k + 1) - f k)) x ∂μ =
    ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ -
      ∫ (x : Ω), (∑ k ∈ Finset.range n, upcrossingStrat a b f N k * (f (k + 1) - f k)) x ∂μ
⊢ ∫ (x : Ω), (∑ k ∈ Finset.range n, (f (k + 1) - f k)) x ∂μ ≤ ∫ (x : Ω), f n x ∂μ - ∫ (x : Ω), f 0 x ∂μ
state_after: no goals
tactic: simp_rw [Finset.sum_range_sub, integral_sub' (hf.integrable _) (hf.integrable _), le_refl]