A
perturbation theorem for linear Hamiltonian systems with bounded orbits 
with Roberta Fabbri
and Ana M. Sanz, 
Discrete Cont. Dyn. Sys. - Ser. A 
13 (3) (2005), 623-635.
The paper concerns the
Sacker-Sell spectral decomposition of a one-parametric
perturbation of a non-autonomous linear Hamiltonian system with bounded
solutions.
Conditions ensuring the continuous variation with respect to the parameter of
the 
spectral intervals and subbundles are established. These conditions depend on
the 
perturbation direction and are closely related to the topological structure of
the flow 
induced by the initial system on the real and complex Lagrange bundles.