-- Mathlib/Probability/Martingale/BorelCantelli.lean
theorem Submartingale.bddAbove_iff_exists_tendsto [IsFiniteMeasure μ] (hf : Submartingale f ℱ μ)
    (hbdd : ∀ᵐ ω ∂μ, ∀ i, |f (i + 1) ω - f i ω| ≤ R) :
    ∀ᵐ ω ∂μ, BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Proof state:
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
⊢ ∀ᵐ (ω : Ω) ∂μ, BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Tactic:
have hg : Submartingale g ℱ μ :=
  hf.sub_martingale (martingale_const_fun _ _ (hf.adapted 0) (hf.integrable 0))

Result:
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
⊢ ∀ᵐ (ω : Ω) ∂μ, BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Proof state:
case h
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
ω : Ω
⊢ g 0 ω = 0 ω

Tactic:
simp only [g, sub_self, Pi.zero_apply]

Result:
no goals

Proof state:
case h
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
⊢ BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Tactic:
convert hω using 1

Result:
case h.e'_1.a
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
⊢ BddAbove (Set.range fun n => f n ω) ↔ BddAbove (Set.range fun n => g n ω)

case h.e'_2.a
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
⊢ (∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)

Proof state:
case h.e'_2.a.refine_2.intro
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
c : ℝ
hc : Tendsto (fun n => g n ω) atTop (𝓝 c)
⊢ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Tactic:
refine ⟨c + f 0 ω, ?_⟩

Result:
case h.e'_2.a.refine_2.intro
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
c : ℝ
hc : Tendsto (fun n => g n ω) atTop (𝓝 c)
⊢ Tendsto (fun n => f n ω) atTop (𝓝 (c + f 0 ω))

Proof state:
case h.e'_2.a.refine_1.intro
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
c : ℝ
hc : Tendsto (fun n => f n ω) atTop (𝓝 c)
⊢ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)

Tactic:
exact ⟨c - f 0 ω, hc.sub_const _⟩

Result:
no goals

Proof state:
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
⊢ ∀ᵐ (ω : Ω) ∂μ, BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Tactic:
have hgbdd : ∀ᵐ ω ∂μ, ∀ i : ℕ, |g (i + 1) ω - g i ω| ≤ ↑R := by
  simpa only [g, sub_sub_sub_cancel_right]

Result:
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
⊢ ∀ᵐ (ω : Ω) ∂μ, BddAbove (Set.range fun n => f n ω) ↔ ∃ c, Tendsto (fun n => f n ω) atTop (𝓝 c)

Proof state:
case h.e'_1.a.refine_1.intro.intro
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
b : ℝ
hb : b ∈ upperBounds (Set.range fun n => f n ω)
n : ℕ
⊢ f n ω + -f 0 ω ≤ b + |f 0 ω|

Tactic:
exact add_le_add (hb ⟨n, rfl⟩) (neg_le_abs _)

Result:
no goals

Proof state:
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
⊢ ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R

Tactic:
simpa only [g, sub_sub_sub_cancel_right]

Result:
no goals

Proof state:
case h.e'_2.a.refine_2.intro
Ω : Type u_1
m0 : MeasurableSpace Ω
μ : Measure Ω
ℱ : Filtration ℕ m0
f : ℕ → Ω → ℝ
R : ℝ≥0
inst✝ : IsFiniteMeasure μ
hf : Submartingale f ℱ μ
hbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |f (i + 1) ω - f i ω| ≤ ↑R
g : ℕ → Ω → ℝ := fun n ω => f n ω - f 0 ω
hg : Submartingale g ℱ μ
hg0 : g 0 = 0
hgbdd : ∀ᵐ (ω : Ω) ∂μ, ∀ (i : ℕ), |g (i + 1) ω - g i ω| ≤ ↑R
ω : Ω
hω : BddAbove (Set.range fun n => g n ω) ↔ ∃ c, Tendsto (fun n => g n ω) atTop (𝓝 c)
c : ℝ
hc : Tendsto (fun n => g n ω) atTop (𝓝 c)
this : Tendsto (fun k => g k ω + f 0 ω) atTop (𝓝 (c + f 0 ω))
⊢ Tendsto (fun n => f n ω) atTop (𝓝 (c + f 0 ω))

Tactic:
simpa only [g, sub_add_cancel]

Result:
no goals