Vakarchuk, S. B., and K. Yu. Myskin. “Some Problems of Simultaneous Approximation of Functions of Two Variables and Their Derivatives by Interpolation Bilinear Splines”. Ukrains’kyi Matematychnyi Zhurnal 57, no. 2 (February 25, 2005): 147–157. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3583.