A comparison principle for a
class of quasilinear elliptic equations is proved. An application of the comparison
principle is given to prove the uniqueness of solutions of Dirichlet problems for a class
of elliptic equations with jump discontinuous boundary data. The comparison
principle is improved from the one given by Serrin. The uniqueness is proved by
reducing the equation to an associated elliptic equation by viewing the graph of the
solution from the side.