Khoma, N.H. (1998) “Linear periodic boundary-value problem for a second-order hyperbolic equation. II. Quasilinear problem”,
Ukrains’kyi Matematychnyi Zhurnal, 50(12), pp. 1680–1685. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/4787 (Accessed: 14 April 2025).