The main objective of
this paper is to formulate an implicit function theorem for Frechet spaces
which is suitable for nonlinear systems of partial differential equations with
prescribed boundary conditions. The applications are discussed in connection
with deformation theory where such problems arise naturally and are of
fundamental importance. Furthermore, their linearizations are certain second-order
perturbations of second-order elliptic noncoercive boundary value problems. The last
part of the paper deals with developing a general theory which covers these
cases.