È. F. Akhmerova, M. A. Rahmatzoda, T. G. Amangil'din, “Formula for regularized trace of $2m$-order differential operator with periodic boundary conditions”, Izv. Vyssh. Uchebn. Zaved. Mat., 2024, no. 5, 85–90; Russian Math. (Iz. VUZ), 68:5 (2024), 72–76
