Fam Ki An. “Concerning Two Approximate Methods for Solution of the Neumann Nonlinear Problems ”. Ukrains’kyi Matematychnyi Zhurnal 40, no. 5 (August 29, 1988): 619–625. Accessed February 17, 2026. https://umj.imath.kiev.ua/index.php/umj/article/view/8810.