Craig W., Wayne C.E.
Solutions of Nonlinear Wave Equations and
Localization Theory 
(28K, TeX)

ABSTRACT.  In this note we describe a new method for
constructing time periodic 
solutions of nonlinear wave equations of the form
$$
u_{tt} = u_{xx} - g(x,u) \qquad 0 < x < \pi,\;
$$ 
with either periodic or Dirichlet boundary conditions.  Details of
the proof are not provided, but the main ideas are presented,
along with possible extensions of this method.