Theorem: MeasureTheory.upcrossingsBefore_eq_sum
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
hab : a < b
⊢ upcrossingsBefore a b f N ω = ∑ i ∈ Finset.Ico 1 (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
state_after: case pos
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
hab : a < b
hN : N = 0
⊢ upcrossingsBefore a b f N ω = ∑ i ∈ Finset.Ico 1 (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 i

case neg
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
hab : a < b
hN : ¬N = 0
⊢ upcrossingsBefore a b f N ω = ∑ i ∈ Finset.Ico 1 (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
tactic: by_cases hN : N = 0
state_before: case neg
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
hab : a < b
hN : ¬N = 0
⊢ upcrossingsBefore a b f N ω = ∑ i ∈ Finset.Ico 1 (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
state_after: case neg
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
hab : a < b
hN : ¬N = 0
⊢ upcrossingsBefore a b f N ω =
    ∑ i ∈ Finset.Ico (Nat.succ 0) (upcrossingsBefore a b f N ω).succ,
        {n | upperCrossingTime a b f N n ω < N}.indicator 1 i +
      ∑ i ∈ Finset.Ico (upcrossingsBefore a b f N ω).succ N.succ, {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
tactic: rw [← Finset.sum_Ico_consecutive _ (Nat.succ_le_succ zero_le')
    (Nat.succ_le_succ (upcrossingsBefore_le f ω hab))]
state_before: case neg
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
hab : a < b
hN : ¬N = 0
h₁ : ∀ k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1
⊢ upcrossingsBefore a b f N ω =
    ∑ i ∈ Finset.Ico (Nat.succ 0) (upcrossingsBefore a b f N ω).succ,
        {n | upperCrossingTime a b f N n ω < N}.indicator 1 i +
      ∑ i ∈ Finset.Ico (upcrossingsBefore a b f N ω).succ N.succ, {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
state_after: case neg
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
hab : a < b
hN : ¬N = 0
h₁ : ∀ k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1
h₂ :
  ∀ k ∈ Finset.Ico (upcrossingsBefore a b f N ω + 1) (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 0
⊢ upcrossingsBefore a b f N ω =
    ∑ i ∈ Finset.Ico (Nat.succ 0) (upcrossingsBefore a b f N ω).succ,
        {n | upperCrossingTime a b f N n ω < N}.indicator 1 i +
      ∑ i ∈ Finset.Ico (upcrossingsBefore a b f N ω).succ N.succ, {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
tactic: have h₂ : ∀ k ∈ Finset.Ico (upcrossingsBefore a b f N ω + 1) (N + 1),
      {n : ℕ | upperCrossingTime a b f N n ω < N}.indicator 1 k = 0 := by
    rintro k hk
    rw [Finset.mem_Ico, Nat.succ_le_iff] at hk
    rw [Set.indicator_of_not_mem]
    simp only [Set.mem_setOf_eq, not_lt]
    exact (upperCrossingTime_eq_of_upcrossingsBefore_lt hab hk.1).symm.le
state_before: case neg
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
hab : a < b
hN : ¬N = 0
h₁ : ∀ k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1
h₂ :
  ∀ k ∈ Finset.Ico (upcrossingsBefore a b f N ω + 1) (N + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 0
⊢ upcrossingsBefore a b f N ω =
    ∑ i ∈ Finset.Ico (Nat.succ 0) (upcrossingsBefore a b f N ω).succ,
        {n | upperCrossingTime a b f N n ω < N}.indicator 1 i +
      ∑ i ∈ Finset.Ico (upcrossingsBefore a b f N ω).succ N.succ, {n | upperCrossingTime a b f N n ω < N}.indicator 1 i
state_after: no goals
tactic: rw [Finset.sum_congr rfl h₁, Finset.sum_congr rfl h₂, Finset.sum_const, Finset.sum_const,
    smul_eq_mul, mul_one, smul_eq_mul, mul_zero, Nat.card_Ico, Nat.add_succ_sub_one,
    add_zero, add_zero]