  A mixed variational formulation of some problems in $L^2$-based Sobolev
spaces is used to define the Newtonian and layer potentials for the Stokes
system with $L^{\infty}$ coefficients on Lipschitz domains in ${\mathbb R}^3$.
Then the solution of the exterior Dirichlet problem for the Stokes system with
$L^{\infty}$ coefficients is presented in terms of these potentials and the
inverse of the corresponding single layer operator.
