This material is based upon work supported by the National Science Foundation under Grant Nos. DMS-9505049, DMS-9973393, DMS-0139824, and DMS-0513438.
Any opinions, findings and conclusions or recomendations expressed in this mater ial are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

Preprints

L. Dieci and E.S. Van Vleck, Lyapunov and Sacker-Sell Spectral Intervals,
(2003) submitted.

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