On a class of hyperbolic systems with multiple characteristics (Q1269420)

The authors discuss the necessary conditions for the well-posedness of the Cauchy problem for a class of first-order differential system with multiple characteristics. They give the Levi condition about lower-order terms under the assumptions on the principal part, that is, the characteristics of multiplicity are at most 3, the rank at a triple point is \(N-1\), and the localization of the determinant of the principal part is not effectively hyperbolic.