The Cauchy problem for a class of hyperbolic operators with triple characteristics
The author gives both a necessary condition and a sufficient condition for \(C^{\infty}\)-wellposedness of the Cauchy problem for a class of hyperbolic operators with triple characteristic. In comparison with the involutive or effectively hyperbolic case the above both conditions contain the so called Levi conditions imposed on the subprincipal symbol \(P^ s_{m-1}(x,\xi)\). The sufficient condition contains Ivrii-Petkov- Hörmander condition, and the necessary condition contains Ivrii-Petkov condition as special cases.
scientific article; zbMATH DE number 4125930