ON THE CAUCHY PROBLEM FOR HYPERBOLIC OPERATORS WITH TRIPLE CHARACTERISTICS WHOSE COEFFICIENTS DEPEND ONLY ON THE TIME VARIABLE II

In [11] we considered the Cauchy problem for hyperbolic operators with triple characteristics whose coe‰cients depend only on the time variable. And we gave su‰cient conditions for Cy well-posedness. In this paper we shall show that the sufficient conditions given in [11] are also necessary under additional assumptions.