In this paper the Neumann
problem for the nonlinear equation y′′= f(t,y,y′) is studied. A priori bounds
are derived and the results of Granas, Guenther and Lee, are invoked to
obtain existence theorems. The existence theorems are in many cases quite
different from those of the Dirichlet problem, e.g. it is possible to obtain
general existence theorems where f(t,y,y′) can grow very rapidly in the y′
variable.