-- Mathlib/Probability/Martingale/Upcrossing.lean
theorem upcrossingsBefore_eq_sum (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

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
⊢ ∀ k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1), {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1

Tactic:
rintro k hk

Result:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1)
⊢ {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1

Tactic:
rw [Set.indicator_of_mem]

Result:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ 1 k = 1

case h
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ k ∈ {n | upperCrossingTime a b f N n ω < N}

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ 1 k = 1

Tactic:
rfl

Result:
no goals

Proof state:
case h
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ k ∈ {n | upperCrossingTime a b f N n ω < N}

Tactic:
exact upperCrossingTime_lt_of_le_upcrossingsBefore (zero_lt_iff.2 hN) hab
  (Nat.lt_succ_iff.1 hk.2)

Result:
no goals

Proof state:
case neg
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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:
rw [← Finset.sum_Ico_consecutive _ (Nat.succ_le_succ zero_le')
  (Nat.succ_le_succ (upcrossingsBefore_le f ω hab))]

Result:
case neg
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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

Proof state:
case neg
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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:
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]

Result:
no goals

Proof state:
case neg
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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

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

Result:
case neg
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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

Tactic:
by_cases hN : N = 0

Result:
case pos
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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

Proof state:
case h
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
k : ℕ
hk : upcrossingsBefore a b f N ω < k ∧ k < N + 1
⊢ N ≤ upperCrossingTime a b f N k ω

Tactic:
exact (upperCrossingTime_eq_of_upcrossingsBefore_lt hab hk.1).symm.le

Result:
no goals

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
⊢ ∀ 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

Tactic:
rintro k hk

Result:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
k : ℕ
hk : 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

Proof state:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : k ∈ Finset.Ico 1 (upcrossingsBefore a b f N ω + 1)
⊢ {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1

Tactic:
rw [Finset.mem_Ico] at hk

Result:
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
hab : a < b
hN : ¬N = 0
k : ℕ
hk : 1 ≤ k ∧ k < upcrossingsBefore a b f N ω + 1
⊢ {n | upperCrossingTime a b f N n ω < N}.indicator 1 k = 1

Proof state:
case pos
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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:
simp [hN]

Result:
no goals

Proof state:
case h
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
k : ℕ
hk : upcrossingsBefore a b f N ω < k ∧ k < N + 1
⊢ k ∉ {n | upperCrossingTime a b f N n ω < N}

Tactic:
simp only [Set.mem_setOf_eq, not_lt]

Result:
case h
Ω : Type u_1
a b : ℝ
f : ℕ → Ω → ℝ
N : ℕ
ω : Ω
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
k : ℕ
hk : upcrossingsBefore a b f N ω < k ∧ k < N + 1
⊢ N ≤ upperCrossingTime a b f N k ω