1. Aslanyan, A.G., Burenkov, V.I.: Refinement of a theorem of V. V. Morozov. Differ. Uravn. 3(4), 687–691 (1967). (Russian)
2. Aslanyan, A.G., Burenkov, V.I.: The integrability in quadratures of certain systems of linear differential equations. Differ. Uravn. 4(7), 1241–1249 (1968). (Russian)
3. Białas, S., Białas, M.: An algorithm for the calculation of the minimal polynomial. Bull. Polish Acad. Sci. Tech. Sci. 56(4), 391–393 (2008)
4. Coddington, E.A., Carlson, R.: Linear ordinary differential equations. SIAM, Bangkok (1997)
5. Erougin, N.: Une remarque sur l’article de L. Shifner. Izv. Akad. Nauk. SSSR Ser. Mat. 5(4), 377–380 (1941). (Russian)