English
Finite sums of analyticOnNhd functions are analyticOnNhd.
Русский
Конечная сумма аналитических на окрестности функций аналитична на окрестности.
LaTeX
$$$\forall N\,\text{Finset},\ (\forall n\in N,\ AnalyticOnNhd_{\mathfrak k}(f(n),s))\Rightarrow AnalyticOnNhd_{\mathfrak k}\bigl(\lambda z. \sum_{n\in N} f(n)(z)\bigr),s.$$$
Lean4
/-- Finite sums of analytic functions are analytic -/
theorem analyticOnNhd_sum {f : α → E → F} {s : Set E} (N : Finset α) (h : ∀ n ∈ N, AnalyticOnNhd 𝕜 (f n) s) :
AnalyticOnNhd 𝕜 (∑ n ∈ N, f n) s := fun z zs ↦ N.analyticAt_sum (fun n m ↦ h n m z zs)