5 5 65
  The setting 'Gauge invariance ON' leads to the standard 
implementation of the Breit-Wigner formula for  S-channel 
propagators.  Generally it breaks gauge invariance.
   For the case 'Gauge invariance ON' the contribution of
diagram which does not contain Breit-Wigner propagator is
multiplied by the factor

 ( Zero width propagator) /( Breit-Wigner propagator)

This trick corresponds to symbolic summation of all diagram
to common denominator expression and the subsequent substitution
of the Breit-Wigner formula into the denominators. This trick
preserves  all mutual cancellations between diagrams  caused by 
gauge  invariance.  As a defect of this trick it must be 
mentioned that the factor above kills the contribution of 
non-resonance diagrams in the resonance point.
