On the Mixed Problem for a Hyperbolic Equation (Memoirs of the American Mathematical Society, no. 112)

"The aim of this paper is to present existence theorems for the mixed problem for a certain class of hyperbolic operators with boundary conditions. The subject was stimulated by S. Agmon's results (Les équations aux dérivées partielles (Paris, 1962)). He considered operators with constant coefficients in the principal part, and in domains bounded by suitable hyperplanes. We generalize his results to operators with variable coefficients, and to domains bounded by hypersurfaces."--from the author's introduction