Abstract We study the initial value problem for the Davey-Stewartson systems
$$
\cases i\partial_t u+c_0\partial_{x_1}^2u+\partial_{x_2}^2 u =
c_1|u|^2u+c_2u\partial_{x_1}\varphi, \quad (x,t)\in{\bold R}^3,\\
\partial_{x_1}^2\varphi+c_3\partial_{x_2}^2\varphi = \partial_{x_1}|u|^2,\\
u(x,0) = \phi(x),
\endcases
$$
where $c_0,c_3\in{\bold R}$, $c_1,c_2\in{\bold C}$,
$u$ is a complex valued function and $\varphi$ is a real valued function.
The initial data $\phi$ is $\bold C$-valued function on $\bold R^n$,
and usually it belongs to some kind of Sobolev type spaces.
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