Lavrenyuk, S. P., and P. Ya. Pukach. 2007. “Mixed Problem for a Nonlinear Hyperbolic Equation in a Domain Unbounded With Respect to Space Variables”. Ukrains’kyi Matematychnyi Zhurnal 59 (11), 1523–1531. https://umj.imath.kiev.ua/index.php/umj/article/view/3408.