Koval’chuk, Y. A., & Kozachenko, Y. V. (1998). Boundary-value problems with random initial conditions and functional series from subφ (Ω). II. Ukrains’kyi Matematychnyi Zhurnal, 50(7), 897–906. https://umj.imath.kiev.ua/index.php/umj/article/view/4870