  N=2 supersymmetric Yang--Mills theories coupled to matter are considered in
the Wess--Zumino gauge. The supersymmetries are realized nonlinearly and the
anticommutator between two susy charges gives, in addition to translations,
gauge transformations and equations of motion. The difficulties hidden in such
an algebraic structure are well known: almost always auxiliary fields can be
introduced in order to put the formalism off--shell, but still the field
dependent gauge transformations give rise to an infinite dimensional algebra
quite hard to deal with. However, it is possible to avoid all these problems by
collecting into an unique nilpotent operator all the symmetries defining the
theory, namely ordinary BRS, supersymmetries and translations. According to
this method the role of the auxiliary fields is covered by the external sources
coupled, as usual, to the nonlinear variations of the quantum fields. The
analysis is then formally reduced to that of ordinary Yang--Mills theory.
