A. A. Dezin’s problem for inhomogeneous Lavrent’ev–Bitsadze equation

We establish a uniqueness criterion for solution of nonlocal Dezin’s problem for an equation of mixed elliptic-hyperbolic type. The solution is constructed as a sum of a series in eigenfunctions of the corresponding one-dimensional spectral problem. In the proof of its convergence there arises a problem on small denominators arises. Under certain restrictions on the given parameters and functions we prove the convergence of constructed series in the class of regular solutions.