Discrete carleson

theorem discrete_carleson :    ∃ G', MeasurableSet G' ∧ 2 * volume G' ≤ volume G ∧    ∀ f : X → ℂ, Measurable f → (∀ x, ‖f x‖ ≤ F.indicator 1 x) →    ∫⁻ x in G \ G', ‖carlesonSum univ f x‖ₑ ≤    C2_0_2 a nnq * volume G ^ (1 - q⁻¹) * volume F ^ q⁻¹ := by  have exc := exceptional_set (X := X)  rw [zpow_neg_one, ← ENNReal.div_eq_inv_mul] at exc  use G', measurable_G', ENNReal.mul_le_of_le_div' exc; intro f measf hf  classical  calc    _ ≤ ∫⁻ x in G \ G', ‖carlesonSum 𝔓₁ f x‖ₑ + ‖carlesonSum 𝔓₁ᶜ f x‖ₑ := by      refine setLIntegral_mono (by fun_prop) fun x _ ↦ ?_      rw [carlesonSum, ← Finset.sum_filter_add_sum_filter_not _ (· ∈ 𝔓₁ (X := X))]      simp_rw [Finset.filter_filter, mem_univ, true_and, carlesonSum, mem_compl_iff]      apply enorm_add_le    _ = (∫⁻ x in G \ G', ‖carlesonSum 𝔓₁ f x‖ₑ) + ∫⁻ x in G \ G', ‖carlesonSum 𝔓₁ᶜ f x‖ₑ :=      lintegral_add_left (by fun_prop) _    _ ≤ C5_1_2 a nnq * volume G ^ (1 - q⁻¹) * volume F ^ q⁻¹ +        C5_1_3 a nnq * volume G ^ (1 - q⁻¹) * volume F ^ q⁻¹ :=      add_le_add (forest_union hf measf) (forest_complement hf measf)    _ ≤ _ := by      simp_rw [mul_assoc, ← add_mul]      gcongr      norm_cast      apply le_C2_0_2 (four_le_a X) (q_mem_Ioc X)