J. Urbas, OBLIQUE BOUNDARY-VALUE-PROBLEMS FOR EQUATIONS OF MONGE-AMPERE TYPE, Calculus of variations and partial differential equations, 7(1), 1998, pp. 19-39
We prove the existence of classical solutions of elliptic equations of
Monge-Ampere type subject to a semilinear oblique boundary condition
which is a C-1 perturbation of the Neumann boundary condition. Our tec
hniques also allow us to treat fully nonlinear strictly oblique bounda
ry conditions satisfying a concavity condition. Examples show that the
above restrictions on the boundary condition are generally necessary
for the existence of classical solutions.