Cauchy’s Problem

Cauchy’s problem with holomorphic data can be studied at the characteristic points of the hypersurface S carrying Cauchy’s data; (for linear equations, see [4], which improves [3; I]; for non linear equations, see Y. Choquet-Bruhat [1]). In general its solution u is algebroid at those points (but an equation with constant coefficients and constant data on a hyperplane constitutes, from this point of view, an exceptional case!). The solution u can be uniformed by a convenient map.