@techreport{R-90-44,
PSURL = {/publications/cgi-bin/tr-fetch.pl?r-90-44+ps},
ABSTRACTURL = {/publications/cgi-bin/tr-fetch.pl?r-90-44+abstr},
ABSTRACT = {In this paper, we propose a formalization of non-monotonic
reasoning using a three-valued logic based on the strong definitions of Kleene.
Non-monotonic reasoning is the rule rather than the exception when agents,
human or machine, must act where information about the environment is
uncertain or incomplete. Information about the environment is subject to 
change due to external causes, or may simply become outdated. This implies 
that inferences previously made may no longer hold and in turn must be 
retracted along with the revision of other information dependent on the 
retractions.

We start by extending Kleene's three-valued logic with an 
``external negation'' connective (-) where -A is  true when 
A is  false or  unknown. In addition, a default operator 
D is added where  DA is interpreted as ``A is 
true by default''. The addition of the default operator increases the 
expressivity of the language, where statements such as ``A is not a
default'' are directly representable. The logic has an intuitive model 
theoretic semantics without any appeal to the use of a fixpoint semantics
for the default operator. The semantics is based on the notion of 
preferential entailment, where a set of sentences Z, 
preferentially entails a sentence A, if and only if a preferred set of
the models of Z are models of A. We also show that the logic 
belongs to the class of cumulative non-monotonic formalisms which
are a subject of current interest.
},
TITLE = {Preliminary Report: NM3 - A Three-Valued Non-Monotonic Formalism. In J. van Eijck, editor, Logics in AI, European Workshop JELIA '90, Amsterdam, the Netherlands, September 1990, Proceedings, volume 478 of Lecture Notes in Artificial Intelligence, pages 196 - 211, Springer Verlag, 1991},
AUTHOR = {Patrick Doherty},
EMAIL = {patdo@ida.liu.se},
YEAR = {1990},
NUMBER = {R-90-44},
INSTITUTION = ida,
ADDRESS = idaaddr,
IDANR = {LiTH-IDA-R-90-44}