  We studied numerically the validity of the fluctuation theorem, introduced by
Evans,Cohen and Morris and proved by Gallavotti and Cohen, for a 2-dimensional
system of particles maintained in a steady shear flow by Maxwell daemon
boundary conditions (see Chernov and Lebowitz). The theorem was found to hold
if one considers the total phase space contraction $\sigma$ occuring at
collisions with both walls: $\sigma=\sigma^\su+\sigma^\giu$. An attempt to
extend it to more local quantities $\sigma^\su$ and $\sigma^\giu$,
corresponding to the collisions with the top or bottom wall only, gave negative
results. The time decay of the correlations in $\sigma^{\su,\giu}$ was very
slow compared to that of $\sigma$.
