Remove all clauses whose heads contain atoms belonging to T;
R3.
From the remaining clauses remove all the negative premises (they are all
satisfied in S);
and let D be the modified database.
Now consider a positive disjunctive database Ε defined as follows:
E
=
DUSU(7nH
a
),
and let
a
subset M of
Η
Ί
be
a
minimal model of E.
Notice that Μ |α
=
S. Indeed, since consequents of clauses from D belong
to //
a
, the only elements from
H
a
"forced" to
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