  We present a general formalism for simplifying manipulations of spin indices
of massless and massive spinors and vectors in Feynman diagrams. The formalism
is based on covariantly reducing the number of field components in the action
in favor of chiral/self-dual fields. In this paper we concentrate on
calculational simplifications involving fermions in gauge theories by
eliminating half of the components of Dirac spinors. Some results are: (1) We
find reference momenta for massless fermions analogous to those used for
external gauge bosons. (2) Many of the known supersymmetry identities (tree and
one-loop) are seen in a simple manner from the graphs. (3) Manipulations with
external line factrs for massive fermions are unnecessary. (4) Some of the
simplifications for nearly maximally helicity violating gluonic amplitudes are
built into the Feynman rules.
