  A suite of input-to-state stability results are presented for a class of
forced differential inclusions, so-called Lur'e inclusions. As a consequence,
semi-global incremental input-to-state stability results for systems of forced
Lur'e differential equations are derived. The results are in the spirit of the
passivity theorem from control theory as both the linear and nonlinear
components of the Lur'e inclusion (or equation) are assumed to satisfy
passivity-type conditions. These results provide a basis for the analysis of
forced Lur'e differential equations subject to (almost) periodic forcing terms
and, roughly speaking, ensure the existence and attractivity of (almost)
periodic state- and output-responses, comprising another focus of the present
work. One ultimate aim of the study is to provide a robust and rigorous
theoretical foundation for a well-defined and tractable ``frequency response''
of forced Lur'e systems.
