  We study the Hausdorff dimension spectrum for Lyapunov exponents for a class
of interval maps which includes several non-hyperbolic situations. We also
analyze the level sets of points with given lower and upper Lyapunov exponents
and, in particular, with zero lower Lyapunov exponent. We prove that the level
set of points with zero exponent has full Hausdorff dimension, but carries no
topological entropy.
