-- Mathlib/MeasureTheory/Function/LpSpace/Basic.lean
theorem cauchy_tendsto_of_tendsto {f : ℕ → α → E} (hf : ∀ n, AEStronglyMeasurable (f n) μ)
    (f_lim : α → E) {B : ℕ → ℝ≥0∞} (hB : ∑' i, B i ≠ ∞)
    (h_cau : ∀ N n m : ℕ, N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N)
    (h_lim : ∀ᵐ x : α ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))) :
    atTop.Tendsto (fun n => eLpNorm (f n - f_lim) p μ) (𝓝 0)

Proof state:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
⊢ ∀ ε > 0, ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Tactic:
intro ε hε

Result:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
⊢ ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Proof state:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
⊢ ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Tactic:
have h_B : ∃ N : ℕ, B N ≤ ε := by
  suffices h_tendsto_zero : ∃ N : ℕ, ∀ n : ℕ, N ≤ n → B n ≤ ε from
    ⟨h_tendsto_zero.choose, h_tendsto_zero.choose_spec _ le_rfl⟩
  exact (ENNReal.tendsto_atTop_zero.mp (ENNReal.tendsto_atTop_zero_of_tsum_ne_top hB)) ε hε

Result:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
h_B : ∃ N, B N ≤ ε
⊢ ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Proof state:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
h_sub : eLpNorm (f n - f_lim) p μ ≤ liminf (fun m => eLpNorm (f n - f m) p μ) atTop
⊢ liminf (fun m => eLpNorm (f n - f m) p μ) atTop ≤ ε

Tactic:
refine liminf_le_of_frequently_le' (frequently_atTop.mpr ?_)

Result:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
h_sub : eLpNorm (f n - f_lim) p μ ≤ liminf (fun m => eLpNorm (f n - f m) p μ) atTop
⊢ ∀ (a : ℕ), ∃ b ≥ a, eLpNorm (f n - f b) p μ ≤ ε

Proof state:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
⊢ eLpNorm (f n - f_lim) p μ ≤ ε

Tactic:
have h_sub : eLpNorm (f n - f_lim) p μ ≤ atTop.liminf fun m => eLpNorm (f n - f m) p μ := by
  refine eLpNorm_lim_le_liminf_eLpNorm (fun m => (hf n).sub (hf m)) (f n - f_lim) ?_
  refine h_lim.mono fun x hx => ?_
  simp_rw [sub_eq_add_neg]
  exact Tendsto.add tendsto_const_nhds (Tendsto.neg hx)

Result:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
h_sub : eLpNorm (f n - f_lim) p μ ≤ liminf (fun m => eLpNorm (f n - f m) p μ) atTop
⊢ eLpNorm (f n - f_lim) p μ ≤ ε

Proof state:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
h_B : ∃ N, B N ≤ ε
⊢ ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Tactic:
obtain ⟨N, h_B⟩ := h_B

Result:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
⊢ ∃ N, ∀ n ≥ N, eLpNorm (f n - f_lim) p μ ≤ ε

Proof state:
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
x : α
hx : Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
⊢ Tendsto (fun n_1 => (f n + -f n_1) x) atTop (𝓝 ((f n + -f_lim) x))

Tactic:
exact Tendsto.add tendsto_const_nhds (Tendsto.neg hx)

Result:
no goals

Proof state:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
h_sub : eLpNorm (f n - f_lim) p μ ≤ liminf (fun m => eLpNorm (f n - f m) p μ) atTop
⊢ ∀ (a : ℕ), ∃ b ≥ a, eLpNorm (f n - f b) p μ ≤ ε

Tactic:
refine fun N1 => ⟨max N N1, le_max_right _ _, ?_⟩

Result:
case intro
α : Type u_1
E : Type u_4
m0 : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
inst✝ : NormedAddCommGroup E
f : ℕ → α → E
hf : ∀ (n : ℕ), AEStronglyMeasurable (f n) μ
f_lim : α → E
B : ℕ → ℝ≥0∞
hB : ∑' (i : ℕ), B i ≠ ⊤
h_cau : ∀ (N n m : ℕ), N ≤ n → N ≤ m → eLpNorm (f n - f m) p μ < B N
h_lim : ∀ᵐ (x : α) ∂μ, Tendsto (fun n => f n x) atTop (𝓝 (f_lim x))
ε : ℝ≥0∞
hε : ε > 0
N : ℕ
h_B : B N ≤ ε
n : ℕ
hn : n ≥ N
h_sub : eLpNorm (f n - f_lim) p μ ≤ liminf (fun m => eLpNorm (f n - f m) p μ) atTop
N1 : ℕ
⊢ eLpNorm (f n - f (N ⊔ N1)) p μ ≤ ε