  Dual feasible functions (DFFs) have been used to provide bounds for standard
packing problems and valid inequalities for integer optimization problems. In
this paper, the connection between general DFFs and a particular family of
cut-generating functions is explored. We find the characterization of
(restricted/strongly) maximal general DFFs and prove a 2-slope theorem for
extreme general DFFs. We show that any restricted maximal general DFF can be
well approximated by an extreme general DFF.
