\begin{thebibliography}{MUVG86}

\bibitem[ABW88]{ABW86}
K.~R.~Apt, H.~Blair, and A.~Walker.
\newblock Towards a theory of declarative knowledge.
\newblock In J.~Minker, editor, {\it Foundations of Deductive Databases and
  Logic Programming}, pp.~89--148, Morgan Kaufmann, Los Altos, CA, 1988.

\bibitem[AVE82]{AV82}
K.~R.~Apt and M.~H.~van~Emden.
\newblock Contributions to the theory of logic programming.
\newblock {\it JACM}, 29(3):841--862, 1982.

\bibitem[Bry89]{Bry89}
F.~Bry.
\newblock Logic programming as constructiveism: a formalization and its
  application to databases.
\newblock In {\it Eighth {ACM} Symposium on Principles of Database Systems},
  pp.~34--50, 1989.

\bibitem[CH82]{CH82}
A.~Chandra and D.~Harel.
\newblock Structure and complexity of relational queries.
\newblock {\it JCSS}, 25(1):99--128, 1982.

\bibitem[CH85]{CH85}
A.~Chandra and D.~Harel.
\newblock Horn clause queries and generalizations.
\newblock {\it Journal of Logic Programming}, 2(1):1--15, 1985.

\bibitem[Cla78]{Cla78}
K.~L.~Clark.
\newblock Negation as failure.
\newblock In Gallaire and Minker, editors, {\it Logic and Databases},
  pp.~293--322, Plenum Press, New York, 1978.

\bibitem[Dum77]{Dum77}
M.~A.~E.~Dummett.
\newblock {\it Elements of Intuitionism}.
\newblock Clarendon Press, Oxford, 1977.

\bibitem[DK89]{DK89}
Ph.~M.~Dung and K.~Kanchanasut.
\newblock {\it A Natural Semantics for Logic Programs with Negation}.
\newblock Technical Report, Asian Institute of Technology, Bankok 10501,
  Thailand, 1989.
\newblock (manuscript).

\bibitem[Fit85]{Fit85}
M.~Fitting.
\newblock A {K}ripke-{K}leene semantics for logic programs.
\newblock {\it Journal of Logic Programming}, 2(4):295--312, 1985.

\bibitem[Gel87]{Gel87}
M.~Gelfond.
\newblock On stratified autoepistemic theories.
\newblock In {\it Proc.\ AAAI}, 1987.

\bibitem[GL88]{GL88}
M.~Gelfond and V.~Lifschitz.
\newblock The stable model semantics for logic programming.
\newblock In {\it Fifth Int'l Conf.\ Symp.~on Logic Programming},
  pp.~1070--1080, Seattle, 1988.

\bibitem[GS86]{GS86}
Y.~Gurevich and S.~Shelah.
\newblock Fixed-point extensions of first order logic.
\newblock {\it Annals of Pure and Applied Logic}, 32:265--280, 1986.

\bibitem[HM86]{HM86}
S.~Hanks and D.~Mc{D}ermott.
\newblock Default reasoning, nonmonotonic logics, and the frame problem.
\newblock In {\it {AAAI} Conference}, pp.~328--333, 1986.

\bibitem[Imm86]{Imm86}
N.~Immerman.
\newblock Relational queries computable in polynomial time.
\newblock {\it Information and Control}, 68(1):86--104, 1986.

\bibitem[JLL83]{JLL83}
J.~Jaffar, J.-L.~Lassez, and J.~Lloyd.
\newblock Completeness of the negation-as-failure rule.
\newblock In {\it Int'l Joint Conf.~on Artificial Intelligence},
  pp.~500--506, 1983.

\bibitem[Kol90]{Kol90}
P.~G.~Kolaitis.
\newblock The expressive power of stratified programs.
\newblock {\it Information and Computation}, 1990.
\newblock (to appear; also available as UCSC-CRL-89-14 from UC Santa Cruz).

\bibitem[Kun87]{Kun87}
K.~Kunen.
\newblock Negation in logic programming.
\newblock {\it Journal of Logic Programming}, 4(4):289--308, 1987.

\bibitem[Kun88]{Kun88}
K.~Kunen.
\newblock {\it Some Remarks on the Completed Database}.
\newblock Technical Report~775, Univ.\ of Wisconsin, Madison, WI 53706, 1988.
\newblock (Abstract appeared in 5th Int'l Conf.\ Symp.\ on Logic Programming,
  Seattle, Aug.\ 1988).

\bibitem[Lif88]{Lif86}
V.~Lifschitz.
\newblock On the declarative semantics of logic programs with negation.
\newblock In J.~Minker, editor, {\it Foundations of Deductive Databases and
  Logic Programming}, pp.~177--192, Morgan Kaufmann, Los Altos, CA, 1988.

\bibitem[Llo87]{Llo87}
J.~W.~Lloyd.
\newblock {\it Foundations of Logic Programming}.
\newblock Springer-Verlag, New York, 2nd edition, 1987.

\bibitem[LT84]{LT84}
J.~W.~Lloyd and R.~W.~Topor.
\newblock Making {P}rolog more expressive.
\newblock {\it Journal of Logic Programming}, 1(3):225--240, 1984.

\bibitem[Mah88]{Mah86}
M.~J.~Maher.
\newblock Equivalences of logic programs.
\newblock In J.~Minker, editor, {\it Foundations of Deductive Databases and
  Logic Programming}, pp.~388--402, Morgan Kaufmann, Los Altos, CA, 1988.

\bibitem[Mar86]{Mar86}
W.~Marek.
\newblock {\it Stable Theories in Auto\-epi\-stemic Logic}.
\newblock Technical Report, University of Kentucky, 1986.
\newblock (manuscript).

\bibitem[MT88]{MT88}
W.~Marek and M.~Truszczynski.
\newblock {\it Auto\-epi\-stemic Logic}.
\newblock Technical Report, University of Kentucky, 1988.
\newblock (manuscript).

\bibitem[Min82]{Min82}
J.~Minker.
\newblock On indefinite databases and the closed world assumption.
\newblock In {\it Sixth Conference on Automated Deduction}, pp.~292--308,
  Springer-Verlag, New York, 1982.

\bibitem[Moo85]{Moo85}
R.~C.~Moore.
\newblock Semantical considerations on non-monotonic logic.
\newblock {\it Artificial Intelligence}, 28:75--94, 1985.

\bibitem[Mor87]{Mor87}
K.~Morris.
\newblock July 1987.
\newblock Talk at Workshop XP8.3i, Oregon Graduate Center.

\bibitem[MUVG86]{MUV86}
K.~Morris, J.~D.~Ullman, and A.~Van~Gelder.
\newblock Design overview of the {Nail!} system.
\newblock In {\it Third Int'l Conf.\ on Logic Programming}, pp.~554--568,
  1986.

\bibitem[Mos74]{Mos74}
Y.~N.~Moschovakis.
\newblock {\it Elementary Induction on Abstract Structures}.
\newblock North-Holland, New York, 1974.

\bibitem[PP88]{PP88}
H.~Przymusinska and T.~C.~Przymusinski.
\newblock Weakly perfect model semantics for logic programs.
\newblock In {\it Fifth Int'l Conf.\ Symp.~on Logic Programming},
  pp.~1106--1120, Seattle, 1988.

\bibitem[Prz88]{Prz86}
T.~Przymusinski.
\newblock On the declarative semantics of deductive databases and logic
  programs.
\newblock In J.~Minker, editor, {\it Foundations of Deductive Databases and
  Logic Programming}, pp.~193--216, Morgan Kaufmann, Los Altos, CA, 1988.

\bibitem[Prz89]{Prz88c}
T.~C.~Przymusinski.
\newblock Every logic program has a natural stratification and an iterated
  fixed point model.
\newblock In {\it Eighth {ACM} Symposium on Principles of Database Systems},
  pp.~11--21, 1989.

\bibitem[Rei78]{Rei78}
R.~Reiter.
\newblock On closed world databases.
\newblock In Gallaire and Minker, editors, {\it Logic and Databases},
  pp.~55--76, Plenum Press, New York, 1978.

\bibitem[Ros89]{Ros89}
K.~A.~Ross.
\newblock A procedural semantics for well-founded negation in logic programs.
\newblock In {\it Eighth {ACM} Symposium on Principles of Database Systems},
  pp.~22--33, 1989.

\bibitem[RT87]{RT87}
K.~A.~Ross and R.~W.~Topor.
\newblock {\it Inferring Negative Information from Disjunctive Databases}.
\newblock Technical Report~87/1, University of Melbourne, 1987.

\bibitem[Sch87]{Sch87}
J.~S.~Schlipf.
\newblock Negation by securable failure in logic programming.
\newblock 1987.
\newblock (manuscript).

\bibitem[She85]{She85}
J.~C.~Shepherdson.
\newblock Negation as failure, {II}.
\newblock {\it Journal of Logic Programming}, 2(3):185--202, 1985.

\bibitem[She88]{She86}
J.~C.~Shepherdson.
\newblock Negation in logic programming.
\newblock In J.~Minker, editor, {\it Foundations of Deductive Databases and
  Logic Programming}, pp.~19--88, Morgan Kaufmann, Los Altos, CA, 1988.

\bibitem[VEK76]{VK76}
M.~H.~van~Emden and R.~A.~Kowalski.
\newblock The semantics of predicate logic as a programming language.
\newblock {\it JACM}, 23(4):733--742, 1976.

\bibitem[VG90]{VG90a}
A.~Van~Gelder.
\newblock Modeling simultaneous events with default reasoning and tight
  derivations.
\newblock {\it Journal of Logic Programming}, 8(1):41--52, 1990.

\bibitem[VG89a]{VG89a}
A.~Van~Gelder.
\newblock Negation as failure using tight derivations for general logic
  programs.
\newblock {\it Journal of Logic Programming}, 6(1):109--133, 1989.
\newblock Preliminary versions appeared in {\it Third IEEE Symp.~on Logic
  Programming} (1986), and {\it Foundations of Deductive Databases and Logic
  Programming}, J.~Minker, ed., Morgan Kaufmann, 1988.

\bibitem[VG89b]{VG89b}
A.~Van~Gelder.
\newblock The alternating fixpoint of logic programs with negation.
\newblock In {\it Eighth {ACM} Symposium on Principles of Database Systems},
  pp.~1--10, 1989.
\newblock Full version available from UC Santa Cruz as UCSC-CRL-89-39.

\bibitem[VGRS88]{VRS88}
A.~Van~Gelder, K.~A.~Ross, and J.~S.~Schlipf.
\newblock Unfounded sets and well-founded semantics for general logic programs.
\newblock In {\it {ACM} Symposium on Principles of Database Systems},
  pp.~221--230, 1988.

\bibitem[Var82]{Var82}
M.~Y.~Vardi.
\newblock The complexity of relational query languages.
\newblock In {\it 14th ACM Symposium on Theory of Computing}, pp.~137--145,
  1982.

\end{thebibliography}