“…Hryniv and Mykytyuk [20][21][22][23] extended the transformation operator method to the inverse problems for the Sturm-Liouville operators with singular potentials and so generalized a number of classical results to this class of operators. Afterwards, the theory of inverse spectral problems for the second-order differential operators with singular potentials was developed in the studies of Savchuk and Shkalikov [24,25], Freiling et al [26], Mykytyuk and Trush [27], Hryniv and Pronska [28,29], Eckhardt et al [30], Guliyev [31], Bondarenko [32][33][34], etc.…”