Asymptotic behaviour of the discrete spectrum of a quasi-periodic boundary value problem for a two-dimensional hyperbolic equation

This paper is concerned with the asymptotic properties of the discrete spectrum of two-dimensional self-adjoint operators of hyperbolic type. For the operator of the model quasi-periodic boundary value problem associated with a self-adjoint hyperbolic equation with smooth coefficients on a two-dimensional torus we obtain an asymptotic formula for the distribution function of the eigenvalues.
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