For citations:

Sekorin V.S. On undecidability of unary non-nested PFP-operators for one successor function theory. Izvestiya Vysshikh Uchebnykh Zavedenii. Matematika. 2024;(4):89-93. (In Russ.) https://doi.org/10.26907/0021-3446-2024-4-89-93