Feller, M. N. “Boundary-Value Problems for a Nonlinear Hyperbolic Equation With Divergent Part and Levy Laplacian”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 2 (February 25, 2012): 237-244. Accessed April 26, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2570.