  A general formal derivation of the screened massive expansion is provided by
Schwinger-Dyson equations. Some known issues of the expansion are clarified and
a more general framework is established for a natural extension of the method
to two-loop or to amplitudes which are not directly defined by a generating
functional. For instance, a one-loop screened expansion is given for the
effective gauge-parameter-independent gluon propagator which arises from the
pinch-technique.
