**
Below is the ascii version of the abstract for 96-473.
The html version should be ready soon.**Paolo Perfetti.
An infinite-dimensional extension of
a Poincar\'e's result concerning the continuation of periodic orbits.
(84K, tex)
ABSTRACT. We study the existence of periodic solutions for
the infinite-dimensional second order system $\ddot x=V_{x},\
x\in{\bf T}^{{\bf Z}_+}.$
Using the Implicit-Function-Theorem we prove the
existence of time-periodic solutions at \lq\lq high frequencies"; no \lq\lq
smallness condition" on $V(x)$ is required.