H. A. Asatryan, “ANALYSIS OF THE POINT SPECTRUM OF THE STURM-LIOUVILLE OPERATOR WITH CERTAIN BEHAVIOR OF POTENTIAL AT INFINITY”, Proc. YSU A: Phys. Math. Sci., vol. 40, no. 1 (209), pp. 23–28, Mar. 2006, doi: 10.46991/PYSUA.2006.40.1.023.