On a problem for a three-dimensional elliptic equation with Bessel operators

The Keldysh problem for a three-dimensional elliptic equation with three singular coefficients in a rectangular parallelepiped is studied. Based on the property of completeness of systems of eigenfunctions of two one-dimensional spectral problems, a uniqueness theorem is proved. The solution to the problem posed is constructed as the sum of a double Fourier — Bessel series.