KovtunI. I., and FellerM. N. “Boundary-Value Problems for a Nonlinear Hyperbolic Equation With Levy Laplaciana”. Ukrains’kyi Matematychnyi Zhurnal 64, no. 11 (November 25, 2012): 1492-1499. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2675.