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  Substitution of the Breit-Wigner propagators 
for the s-channel virtual particles can break the
gauge invariance of the amplitude. 'Gauge invariance OFF'
denotes the prescription for direct substitution of the
Breit-Wigner propagators which does not take care of
the gauge invariance.
   'Gauge invariance ON' denotes the prescription which
respects the gauge invariance. First the sum of the
diagrams is taken preserving gauge cancellations between 
them, then the Breit-Wigner denominators are substituted 
by multiplication of the entire squared amplitude on the 
factor

 ( Zero width denomonator) /( Breit-Wigner denominator)

for each s-channel resonance. It should be pointed out that
the zero width 'Zero width denomonator' P^2-Mass^2 suppresses 
artificially the contributions of nonresonant diagrams in the 
vicinity of the resonance P^2=M^2. In most cases the total 
cross section error is negligibly small with the only exception 
of overlapping resonances.