For citations:

Nizhnikov A.I., Yaremko O.E., Yaremko N.N., Mukhanov S.A. Combinatorial-analytical method for wave equation with abrupt parameter changes. Chebyshevskii Sbornik. 2025;26(4):344-356. (In Russ.) https://doi.org/10.22405/2226-8383-2025-26-4-344-356