Introduction to BRS symmetry
  This paper contains a revised version of the lecture notes of a short course on the quantization of gauge theories. Starting from a sketchy review of scattering theory, the paper describes the lines of BRST-Faddeev-Popov quantization considering the problem of a non-perturbative extension of this method. The connection between Slavnov-Taylor identity and S-matrix unitarity is also discussed. 
Carlo Becchi