I. V. Kremleva, “A method for constructing asymptotic solutions of differential
equations”, Dokl. Akad. Nauk, 328:3 (1993), 289–291; Dokl. Math., 47:1 (1993), 68–72
2.
I. V. Kremleva, B. Yu. Sternin, V. E. Shatalov, “On the multiplicative power asymptotics of solutions of wave equations”, Differ. Uravn., 29:11 (1993), 1984–1995; Differ. Equ., 29:11 (1993), 1722–1732
