Wave fronts of solutions of some classes of non-linear partial differential equations
1. This paper is devoted to the study of wave fronts of solutions of first order symmetric systems of non-linear partial differential equations. A short communication was published in . The microlocal point of view enables us to obtain more precise information concerning the smoothness of solutions of symmetric hyperbolic systems. Our main result is a generalization to the non-linear case of Theorem 1.1 of Ivriĭ . The machinery of paradifferential operators introduced by Bony  together with an idea coming from ,  are used.