The implementation orients on the diploma thesis of Mirja Boehmer
in this class a variant of the approach
"A Preference-Based Framework for Updating Logic Programs" by James P.
Delgrande, Torsten Schaub and Hans Tompits is implemented, respectively the
operator *1 is used; first step: defaultification of two given programs
second step: computation of the answer sets of the concatenation of the two
defaulticated programs third step: computation of the revised program with
the help of these answer sets last step: computation of the answer sets of
the revised program
We are only check for conflicting rules and remove this rules with lesser priority.