LavrenyukS. P., and OliskevychM. O. “Mixed Problem for a Semilinear Ultraparabolic Equation in an Unbounded Domain”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, no. 12, Dec. 2007, pp. 1661–1673, https://umj.imath.kiev.ua/index.php/umj/article/view/3420.