In this paper we consider hyperbolic systems of linear, homogeneous, first order partial differential equations with variable coefficients. We will say that the Cauchy initial value problem for such a ...

Suppose that the linear partial differential operator P(x, D) has analytic coefficients and that it can be written in the form P(x, D) = R(x, D)S(x, D) where S(x, D) is a polynomial in the homogeneous ...