Посилання:On a Convergence of Formal Power Series Under a Special Condition on the Gelfond-Leont'ev Derivatives / M.M. Sheremeta, O.A. Volokh // Журнал математической физики, анализа, геометрии. — 2007. — Т. 3, № 2. — С. 241-252. — Бібліогр.: 3 назв. — англ.
For a formal power series the conditions on the Gelfond-Leont'ev derivatives are found, under which the series represents a function, analytic in the disk {z : |z| < R}, 0 < R ≤ +∞.