The objective of this paper is to establish
explicitly with using localization hypothesis, some algebraically
conditions of decomposition of a system of partial differential
equations with multiple characteristics and pair multiplicity.
These conditions are sufficient for the well posedness of the
associated Cauchy problem. The technic of the
asymptotically solutions prove that these conditions are also
necessary.
Key Words: Problème de Cauchy , hyperbolicité, décomposition d'un opérateur, parametrix.