Stability of a solution to one combined mixed problem for the Klein–Gordon–Fock equation with a variable coefficient

The paper studies one combined mixed problem for the Klein–Gordon–Fock equation with a variable coefficient. The solvability of the problem under consideration is proved. In addition to solvability, it is also substantiated that the solution to the studied mixed problem is stable with respect to an additive perturbation of the coefficient, as well as with respect to the boundary conditions and the right-hand side of the equation.