  The domain wall fermion formulation exhibits full chiral symmetry for finite
lattice spacing except for the effects of mixing between the domain walls.
Close to the continuum limit these symmetry breaking effects should be
described by a single residual mass. We determine this mass from the
conservation law obeyed by the conserved axial current in quenched simulations
with beta=5.7 and 6.0 and domain wall separations varying between 12 and 48 on
8^3x32 and 16^3x32 lattices. Using the resulting values for the residual mass
we perform two complete and independent calculations of the pion decay
constant. Good agreement is found between these two methods and with
experiment.
