For phenomenology of High Energy Physics experiments, Known Physics
and New Physics phenomena, predictions need to be available.
One has to take into account results of diverse research activities. On experiments
side this includes control of
detector acceptance and its response details, also observable
definitions and different types of background subtractions. On theoretical
side one needs to keep in mind results on:
higher order matrix elements calculations, structure functions, evolution
kernels, Monte Carlo and/or semi-analytic integration algorithms,
algebraic manipulation programs.

I will not address foundations of Yennie-Frautchi-Suura exclusive
exponentiation, or of factorizations used in QCD. That would be too
broad a subject, obscuring the main purpose of my talk. I will concentrate
on the investigation of spin amplitude gauge invariant parts and how
they were useful in case of my work.