  Lyapunov's indirect method is an attractive method for analyzing stability of
non-linear systems since only the stability of the corresponding linearized
system needs to be determined. Unfortunately, the proof for finite-dimensional
systems does not generalize to infinite-dimensions. In this paper a unified
approach to Lyapunov's indirect method for infinite-dimensional system is
described. It is shown how existing sufficient conditions fit this framework
and a new sufficient condition is presented.
