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  In many processes the matrix element squared 
is too singular for efficient Monte Carlo integration.
  Propagators of intermediate particles cause the
s-channel and t-channel peaks of the amplitude. They
can be explicitly indicated to the integration program
to ensure efficient integration with meaningful result.

  The regularization program is efficient if the
phase space parametrization is properly chosen.
  Regularization of a singularity which leads to infinite 
cross section (e.g. the t-channel gamma pole) should be
associated with a kinematics cut for the corresponding 
momentum squared ('S'-type cut). The regularization 
program is sensitive only to this type of cuts since they
reduce the phase space regions with divergences of the
amplitude.