This paper is concerned with the nonlinear Davey-Stewartson equations
which are of different type according to the signs of and m respectively. There are several special cases of this system which can be treated by an inverse scattering method, but this paper deals with the general case. In a first chapter there is given a brief motivation of these equations as a model for the propagation of water waves in an impermeable and horizontal bed of infinite extent. Moreover some relevant conservation laws - like conservation of mass, momentum and energy - are derived and also the interesting relation
which has already been noticed by Ablowitz and Segur. Here E(u(t)) (the energy) is a specific constant of motion. This relation is used for the proof of a blow up result for solutions.
In the second chapter the Cauchy problem in the case is studied. Here is an existence and uniqueness result in a finite time interval which may be infinite if the Cauchy data are sufficiently small. Furthermore regularity and continuous dependence of solutions from data are studied. In the third chapter nonexistence results are emphasized as for example in the case for the solutions exist global in time and for there is a blow up in finite time. Chapter four is devoted to prove existence in the case and . The proofs are sometimes short and only indicated. The results of the paper had been announced by the authors [C. R. Acad. Sci., Paris, Sér. I 308, No.4, 115-120 (1989; Zbl 0656.76012)].