  The Gallavotti-Cohen fluctuation theorem suggests a general symmetry in the
fluctuations of the entropy production, a basic concept in the theory of
irreversible processes, based on results in the theory of strongly chaotic
maps.
  We study this symmetry for some standard models of nonequilibrium steady
states. We give a general strategy to derive a 'local' fluctuation theorem
exploiting the Gibbsian features of the stationary space-time distribution.
This is applied to spin flip processes and to the asymmetric exclusion process.
