S. Nigiyan, “ON $\lambda$-DEFINABILITY OF ARITHMETICAL FUNCTIONS WITH INDETERMINATE VALUES OF ARGUMENTS”, Proc. YSU A: Phys. Math. Sci., vol. 50, no. 2 (240), pp. 39–47, Jun. 2016, doi: 10.46991/PSYU:A/2016.50.2.039.