Solutions for systems of nonlinear elliptic equations with nonlinear boundary conditions
Franz Rothe, Karl Peter Hadeler · Mathematical Methods in the Applied Sciences · 1979
Abstract We look for solutions of systems of nonlinear elliptic equations with nonlinear boundary conditions and values in some compact convex set M. If the nonlinear terms satisfy a sign condition on the boundary of M and the inhomogeneous terms assume their values in this set existence of solutions is proved. The proof is based on the homotopy invariance of the Leray‐Schauder degree and Weinberger's strong maximum principle.