For a nonlinear Anosov diffeomorphism $a$ of the 2-torus, we present examples
of equilibrium states $\mu$ such that the group of $\mu$-preserving
diffeomorphism is virtually cyclic. We then present a larger class of
$a$-invariant measures for which the set of entropies for all $C^{1+\alpha}$
diffeomorphisms is a semi-group isomorphic $\N$.
We prove a result motivated by Williams's classification of expanding
attractors and the Franks-Newhouse Theorem on codimension-1 Anosov
diffeomorphisms: If a mixing hyperbolic attractor has 1-dimensional unstable
manifolds then it is either is expanding or is homeomorphic to a compact
abelian group (a toral solenoid); in the latter case the dynamics is conjugate
to a group automorphism. As a corollary we obtain a classification of all
2-dimensional basic sets in 3-manifolds.