MentynskyiS. M., and ShuvarB. A. “Two-Sided Approximation of Solutions of Boundary-Value Problems”. Ukrains’kyi Matematychnyi Zhurnal 57, no. 2 (February 25, 2005): 284–288. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3597.