1. Romanovskii R. K., “On Riemann matrices of the first and second kind,” Dokl. Akad. Nauk SSSR, 267, No. 3, 577–580 (1982).
2. Romanovskii R. K., “Exponentially splittable hyperbolic systems in two independent variables, ” Mat. Sb., 133, No. 3, 341–355 (1987).
3. Romanovskii R. K., “The monodromy operator of a hyperbolic system with periodic coefficients, ” in: Application of Methods of Functional Analysis in Problems of Mathematical Physics [in Russian], Akad. Nauk Ukrain. SSR, Inst. Mat. (Kiev), Kiev, 1987, pp. 47–52.
4. Romanovskii R. K., “Averaging of hyperbolic equations,” Dokl. Akad. Nauk SSSR, 306, No. 2, 286–289 (1989).
5. Romanovskii R. K., “On Riemann matrices of the first and second kind,” Mat. Sb., 127, No. 4, 494–501 (1985).