N. A. Chernyavskaya, L. A. Shuster, “A representation of solutions of the Sturm–Liouville equation and its applications”, Differ. Uravn., 28:3 (1992), 537–540
1989
2.
N. A. Chernyavskaya, L. A. Shuster, “The WKB method”, Differ. Uravn., 25:10 (1989), 1826–1829
