Khoma, N. H. “Linear Periodic Boundary-Value Problem for a Second-Order Hyperbolic Equation. II. Quasilinear Problem”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 12 (December 25, 1998): 1680–1685. Accessed May 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4787.