  This paper is about the stabilization of a cascade system composed by an
infinite-dimensional system, that we suppose to be exponentially stable, and an
ordinary differential equation (ODE), that we suppose to be marginally stable.
The system is controlled through the infinite-dimensional system. Such a
structure is particularly useful when applying the internal model approach on
infinite-dimensional systems. Our strategy relies on the forwarding method,
which uses a Lyapunov functional and a Sylvester equation to build a
feedback-law. Under some classical assumptions in the output regulation theory,
we prove that the closed-loop system is globally exponentially stable.
