1. V. V. Katrakhov and S. M. Sitnik, ‘‘The transmutation method and boundary–value problems for singular elliptic equations,’’’ Contemp. Math. Fundam. Dir. 4, 211–428 (2018) [in Russian].
2. A. V. Glushak, ‘‘Transmutation operators as a solvability concept of abstract singular equations,’’ in Transmutation Operators and Applications, Trends in Mathematics (Springer, Birkhäuser, 2020), pp. 379–410.
3. A. V. Glushak, ‘‘The Bessel operator function,’’ Dokl. Math. 55, 103–105 (1997).
4. A. V. Glushak and O. A. Pokruchin, ‘‘Criterion for the solvability of the Cauchy problem for an abstract Euler–Poisson–Darboux equation,’’ Differ. Equat. 52, 39–57 (2016).
5. A. V. Glushak, ‘‘A family of Bessel operator functions. Geometry and mechanics,’’ Itogi Nauki Tekh., Ser. Sovrem. Mat. Prilozh. 187, 36–43 (2020).