We construct a number of lattice fermions, which fulfill the Ginsparg-Wilso
n relation either exactly or approximately, and test them in the framework
of the 2-flavor Schwinger model. We start from explicit approximations with
in a short range, and study this formulation, as well as its correction to
an exact Ginsparg-Wilson fermion by the "overlap formula". Then we suggest
a new method to realize this correction perturbatively, without using the t
edious square root operator. In this way we combine many favorable properti
es: good chiral behavior, small mass renormalization, excellent scaling and
rotational invariance, as well as a relatively modest computational effort
, which makes such formulations most attractive for QCD. (C) 2000 Elsevier
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