Generic area-preserving reversible diffeomorphisms

Abstract

Let M be a surface and R : M -> M an area-preserving C-infinity diffeomorphism which is an involution and whose set of fixed points is a submanifold with dimension one. We will prove that C-1 - generically either an area-preserving R-reversible diffeomorphism, is Anosov, or, for mu-almost every x is an element of M, the Lyapunov exponents at x vanish or else the orbit of x belongs to a compact hyperbolic set with an empty interior. We will also describe a nonempty C-1-open subset of area-preserving R-reversible diffeomorphisms where for C-1 - generically each map is either Anosov or its Lyapunov exponents vanish from almost everywhere.