. rcases this with ⟨h_center, h_sides⟩
  simp [Metric.tendsto_atTop] at h_sides
  specialize h_sides (ε/2) (half_pos hε)
  rcases h_center with ⟨N_center, h_center⟩
  rcases h_sides with ⟨N_sides, h_sides⟩
  exists max N_center N_sides
  intro n hn
  specialize h_center n (le_of_max_le_left hn)
  specialize h_sides n (le_of_max_le_right hn)
  rw [← add_halves' ε]
  refine lt_of_le_of_lt ?_ (add_lt_add h_center h_sides)
  clear h_center h_sides hn N_center N_sides  have hδδ : -δ ≤ δ := by simp [hδ.le]
  simp [integral_eq_add_Iic_Ioc_Ioi h_integrable hδδ]
  conv =>
    lhs; arg 1
    conv => lhs; rw [add_comm]
    rw [add_assoc]
  refine le_trans (abs_add _ _) ?_
  simp
  refine le_of_eq ?_
  congr
  simp [integral_union, Set.Iic_disjoint_Ioi hδδ, h_integrable.integrableOn]
case h_tendsto.intro.intro
φ : ℝ → ℝ
hφ : IsBump φ
h_integrable : ∀ {n : ℕ+}, Integrable fun x => (φ x - φ 0) * DiracSeq (↑↑n) x
ε : ℝ
hε : 0 < ε
δ : ℝ
hδ : 0 < δ
hδε : ∀ {x : ℝ}, |x| < δ → |φ x - φ 0| < ε / 2
this :
  (∃ N, ∀ (n : ℕ+), N ≤ n → |∫ (x : ℝ) in Set.Ioc (-δ) δ, (φ x - φ 0) * DiracSeq (↑↑n) x| < ε / 2) ∧
    Tendsto (fun n => ∫ (x : ℝ) in Set.Iic (-δ) ∪ Set.Ioi δ, (φ x - φ 0) * DiracSeq (↑↑n) x) atTop (nhds 0)
⊢ ∃ N, ∀ (n : ℕ+), N ≤ n → |∫ (x : ℝ), (φ x - φ 0) * DiracSeq (↑↑n) x| < ε

case this
φ : ℝ → ℝ
hφ : IsBump φ
h_integrable : ∀ {n : ℕ+}, Integrable fun x => (φ x - φ 0) * DiracSeq (↑↑n) x
ε : ℝ
hε : 0 < ε
δ : ℝ
hδ : 0 < δ
hδε : ∀ {x : ℝ}, |x| < δ → |φ x - φ 0| < ε / 2
⊢ (∃ N, ∀ (n : ℕ+), N ≤ n → |∫ (x : ℝ) in Set.Ioc (-δ) δ, (φ x - φ 0) * DiracSeq (↑↑n) x| < ε / 2) ∧
    Tendsto (fun n => ∫ (x : ℝ) in Set.Iic (-δ) ∪ Set.Ioi δ, (φ x - φ 0) * DiracSeq (↑↑n) x) atTop (nhds 0)
case this
φ : ℝ → ℝ
hφ : IsBump φ
h_integrable : ∀ {n : ℕ+}, Integrable fun x => (φ x - φ 0) * DiracSeq (↑↑n) x
ε : ℝ
hε : 0 < ε
δ : ℝ
hδ : 0 < δ
hδε : ∀ {x : ℝ}, |x| < δ → |φ x - φ 0| < ε / 2
⊢ (∃ N, ∀ (n : ℕ+), N ≤ n → |∫ (x : ℝ) in Set.Ioc (-δ) δ, (φ x - φ 0) * DiracSeq (↑↑n) x| < ε / 2) ∧
    Tendsto (fun n => ∫ (x : ℝ) in Set.Iic (-δ) ∪ Set.Ioi δ, (φ x - φ 0) * DiracSeq (↑↑n) x) atTop (nhds 0)