English
A finite sum of analyticOn functions is analyticOn.
Русский
Конечная сумма аналитических на множестве функций аналитична на множестве.
LaTeX
$$$\forall N\,\text{Finset},\ (\forall n\in N,\ AnalyticOn_{\mathfrak k}(f(n),s))\Rightarrow AnalyticOn_{\mathfrak k}\Bigl(\lambda z. \sum_{n\in N} f(n)(z)\Bigr),s.$$$
Lean4
/-- Finite sums of analytic functions are analytic -/
theorem analyticOn_fun_sum {f : α → E → F} {s : Set E} (N : Finset α) (h : ∀ n ∈ N, AnalyticOn 𝕜 (f n) s) :
AnalyticOn 𝕜 (fun z ↦ ∑ n ∈ N, f n z) s := fun z zs ↦ N.analyticWithinAt_fun_sum (fun n m ↦ h n m z zs)