  The equivalence of domain wall and overlap fermion formulations is
demonstrated for lattice gauge theories in 2+1 spacetime dimensions with
parity-invariant mass terms. Even though the domain wall approach distinguishes
propagation along a third direction with projectors ${1\over2}(1\pm\gamma_3)$,
the truncated overlap operator obtained for finite wall separation $L_s$ is
invariant under interchange of $\gamma_3$ and $\gamma_5$. In the limit
$L_s\to\infty$ the resulting Ginsparg-Wilson relations recover the expected
U($2N_f$) global symmetry up to O($a$) corrections. Finally it is shown that
finite-$L_s$ corrections to bilinear condensates associated with dynamical mass
generation are characterised by whether even powers of the symmetry-breaking
mass are present; such terms are absent for antihermitian bilinears such as
$i\bar\psi\gamma_3\psi$, markedly improving the approach to the large-$L_s$
limit.
