KhomaN. H., and KhomaL. G. “A Linear Periodic Boundary-Value Problem for a Second-Order Hyperbolic Equation”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 2 (February 25, 1999): 281–284. Accessed October 6, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4611.