We observe that p(2) is in all models. However, the rule-based semantics
leaves a, and hence p, completely unclassified. The problem is that one of the
cases set{a(2),
—ια(2)}
must hold but the semantics is not powerful enough to
use this information. •
Tree-oriented
Semantics
for
Negation
as
Failure
In this section we consider semantics in which remaining rules sets (RR
k
) are
replaced by sets of "remaining proof trees." First we define a simple tree
semantics that is equivalent to the rule semantics of Definition 5 in the sense
that it produces the same SS
k
and FS
k
. Then we propos
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