1. L. S. Pulkina and E. N. Klimova, ‘‘A nonlocal boundary value problem for a nonlinaer one dimensional wave equation,’’ Mat. Model. Kraev. Zadachi 3, 192–195 (2006).
2. T. I. Kiguradze, ‘‘Periodic boundary value problems for linear hyperbolic equations. I,’’ Differ. Uravn. 29, 281–297 (1993).
3. T. I. Kiguradze, ‘‘Periodic boundary value problems for linear hyperbolic equations. II,’’ Differ. Uravn. 29, 637–645 (1993).
4. T. Kiguradze, ‘‘Some boundary value problems for systems of linear partial differential equations of hyperbolic type,’’ Mem. Differ. Equat. Math. Phys. 1, 1–144 (1994).
5. T. I. Kiguradze, ‘‘On periodic in the plane solutions of second order hyperbolic systems,’’ Arch. Math. 33, 253–272 (1997).