  We continue the investigation of quantized Yang-Mills theories coupled to
matter fields in the framework of causal perturbation theory which goes back to
Epstein and Glaser. In this approach gauge invariance is expressed by a simple
commutator relation for the S-matrix and the corresponding gauge
transformations are simple transformations of the free fields only. In spite of
this simplicity, gauge invariance implies the usual Slavnov-Taylor identities.
The main purpose of this paper is to prove the latter statement. Since the
Slavnov-Taylor identities are formulated in terms of Green's functions, we
investigate the agreement of two perturbative definitions of Green's functions,
namely of Epstein and Glaser's definition with the Gell-Mann Low series.
