  A mixed boundary value problem for the Stokes system in a polyhedral domain
is considered. Here different boundary conditions (in particular, Dirichlet,
Neumann, free surface conditions) are prescribed on the sides of the
polyhedron. The authors prove the existence of solutions in (weighted and
non-weighted) $L_p$ Sobolev spaces and obtain regularity assertions for weak
solutions. The results are based on point estimates of Green's matrix.
