  In this paper, we propose a new derivation for the Green-Kubo relationship
for the liquid-solid friction coefficient, characterizing hydrodynamic slippage
at a wall. It is based on a general Langevin approach for the fluctuating wall
velocity, involving a non-markovian memory kernel with vanishing time integral.
The calculation highlights some subtleties of the wall-liquid dynamics, leading
to superdiffusive motion of the fluctuating wall position.
