have l1 : ∀ᶠ (p : ℝ × ℕ) in 𝓝[>] 0 ×ˢ atTop, C * ⌈p.1 * p.2⌉₊ / p.2 < δ := by
  have r1 := tendsto_mul_ceil_div.const_mul C
  simp [mul_div_assoc'] at r1 ; exact r1 (Iio_mem_nhds hδ)
case intro
n : ℕ
A a b c d u x y t σ' : ℝ
ψ Ψ : ℝ → ℂ
F G : ℂ → ℂ
f✝ : ℕ → ℂ
𝕜 : Type
inst✝ : _root_.RCLike 𝕜
f : ℕ → ℝ
hpos : 0 ≤ f
δ : ℝ
hδ : δ > 0
C : ℝ
hC : chebyWith C fun n => ↑(f n)
⊢ ∀ᶠ (n : ℝ × ℕ) in 𝓝[>] 0 ×ˢ atTop, dist (S f 0 n.2) (S f n.1 n.2) < δ
case intro
n : ℕ
A a b c d u x y t σ' : ℝ
ψ Ψ : ℝ → ℂ
F G : ℂ → ℂ
f✝ : ℕ → ℂ
𝕜 : Type
inst✝ : _root_.RCLike 𝕜
f : ℕ → ℝ
hpos : 0 ≤ f
δ : ℝ
hδ : δ > 0
C : ℝ
hC : chebyWith C fun n => ↑(f n)
l1 : ∀ᶠ (p : ℝ × ℕ) in 𝓝[>] 0 ×ˢ atTop, C * ↑⌈p.1 * ↑p.2⌉₊ / ↑p.2 < δ
⊢ ∀ᶠ (n : ℝ × ℕ) in 𝓝[>] 0 ×ˢ atTop, dist (S f 0 n.2) (S f n.1 n.2) < δ