  We first give an overview of the basic theory for discrete unital twisted
C*-dynamical systems and their covariant representations on Hilbert C*-modules.
After introducing the notion of equivariant representations of such systems and
their product with covariant representations, we prove a kind of Fell
absorption principle saying that the product of an induced regular equivariant
representation with a covariant faithful representation is weakly equivalent to
an induced regular covariant representation. This principle is the key to our
main result, namely that a certain property, formally weaker than Exel's
approximation property, ensures that the system is regular, i.e., the
associated full and reduced C*-crossed products are canonically isomorphic.
