English
If k is at least 3, then for each z in the upper half-plane, the family x ↦ |eisSummand(k,x,z)| is summable over x ∈ Fin(2 → ℤ).
Русский
При k ≥ 3 для любой z в верхней полуплоскости семейство x ↦ |eisSummand(k,x,z)| сходится по сумме по x ∈ Fin(2 → ℤ).
LaTeX
$$$\text{Summable}_{x:Fin(2\to\mathbb{Z})} \|\mathrm{eisSummand}(k,x,z)\|,$ если $3 \le k$.$$
Lean4
theorem summable_norm_eisSummand {k : ℤ} (hk : 3 ≤ k) (z : ℍ) : Summable fun (x : Fin 2 → ℤ) ↦ ‖(eisSummand k x z)‖ :=
by
have hk' : (2 : ℝ) < k := by norm_cast
apply ((summable_one_div_norm_rpow hk').mul_left <| r z ^ (-k : ℝ)).of_nonneg_of_le (fun _ ↦ norm_nonneg _)
intro b
simp only [eisSummand, norm_zpow]
exact_mod_cast summand_bound z (show 0 ≤ (k : ℝ) by positivity) b