S. R. Gordeev, “On the index and the homotopic classification of Noetherian operators with a finite group of shifts”, Funktsional. Anal. i Prilozhen., 25:1 (1991), 66–68; Funct. Anal. Appl., 25:1 (1991), 53–55
1990
2.
S. R. Gordeev, “The index of operators with shift, and cyclic subgroups”, Mat. Zametki, 48:1 (1990), 146–148
