The Vector Equivalence Technique
  We present the Vector Equivalence technique. This technique allows a simple and systematic calculating of Feynman diagrams involving massive fermions at the matrix element level. As its name suggests, the technique allows two Lorentz four-vectors to serve as an equivalent of two external fermions. In further calculations, traces involving these vectors replace the matrix element with the external fermions. The technique can be conveniently used for both symbolic and numeric calculations. 
E. Yehudai