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  CalcHEP provides you with a
possibility to apply Weizsacker-
Williams approximation to
processes of electro-production
for the case of small angle of
scattering of charged particle. 
In this case one can reduce
electro-production process to the
photo-production one with an
appropriate photon spectrum. The
resulting  spectrum depends on
maximum value of photon
virtualities taking into account.
