Sardarian, V.T. (2000) “ESTIMATES FOR EIGENVALUES AND COMPLETENESS OF EIGENFUNCTIONS OF NON SELFADJOINT SEMIELLIPTIC DIFLERENTIAL OPERATORS”, Proceedings of the YSU A: Physical and Mathematical Sciences, 34(2 (193), pp. 10–18. doi:10.46991/PYSUA.2000.34.2.010.