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

We establish a criterion for the uniqueness of a solution to nonlocal Dezin's problem for an equation of mixed elliptic-hyperbolic type. The solution is constructed in the form of a sum of a series in eigenfunctions of the corresponding one-dimensional spectral problem. In substantiation of the convergence of series a problem of small denominators arizes. Under certain specified conditions with respect to given pagameters and functions we prove the convergence of constructed series in a class of regular solutions.