26,786 research outputs found
Complexity of Nested Circumscription and Nested Abnormality Theories
The need for a circumscriptive formalism that allows for simple yet elegant
modular problem representation has led Lifschitz (AIJ, 1995) to introduce
nested abnormality theories (NATs) as a tool for modular knowledge
representation, tailored for applying circumscription to minimize exceptional
circumstances. Abstracting from this particular objective, we propose L_{CIRC},
which is an extension of generic propositional circumscription by allowing
propositional combinations and nesting of circumscriptive theories. As shown,
NATs are naturally embedded into this language, and are in fact of equal
expressive capability. We then analyze the complexity of L_{CIRC} and NATs, and
in particular the effect of nesting. The latter is found to be a source of
complexity, which climbs the Polynomial Hierarchy as the nesting depth
increases and reaches PSPACE-completeness in the general case. We also identify
meaningful syntactic fragments of NATs which have lower complexity. In
particular, we show that the generalization of Horn circumscription in the NAT
framework remains CONP-complete, and that Horn NATs without fixed letters can
be efficiently transformed into an equivalent Horn CNF, which implies
polynomial solvability of principal reasoning tasks. Finally, we also study
extensions of NATs and briefly address the complexity in the first-order case.
Our results give insight into the ``cost'' of using L_{CIRC} (resp. NATs) as a
host language for expressing other formalisms such as action theories,
narratives, or spatial theories.Comment: A preliminary abstract of this paper appeared in Proc. Seventeenth
International Joint Conference on Artificial Intelligence (IJCAI-01), pages
169--174. Morgan Kaufmann, 200
Global Physics: From Percolation to Terrorism, Guerilla Warfare and Clandestine Activities
The September 11 attack on the US has revealed an unprecedented terrorism
with worldwide range of destruction. It is argued to result from the first
worldwide percolation of passive supporters. They are people sympathetic to the
terrorism cause but without being involved with it. They just don't oppose it
in case they could. This scheme puts suppression of the percolation as the
major strategic issue in the fight against terrorism. Acting on the population
is shown to be useless. Instead a new strategic scheme is suggested to increase
the terrorism percolation threshold and in turn suppress the percolation. The
relevant associated space is identified as a multi-dimensional social space
including both the ground earth surface and all various independent flags
displayed by the terrorist group. Some hints are given on how to shrink the
geographical spreading of terrorism threat. The model apply to a large spectrum
of clandestine activities including guerilla warfare as well as tax evasion,
corruption, illegal gambling, illegal prostitution and black markets.Comment: 17 pages, 7 figures, Proceedings of the International Workshop
Randomness And Complexity in honor of Shlomo Havlin's 60th birthday held in
January 2003, Eilat, Israe
Interrogating the Migration Industry
Review of Ruben Andersson,Illegality, Inc. (Oakland, CA: University of California Press, 2014)and Amy Nethery and Stephanie J. Silverman(eds.), Immigration Detention: The Migration of a Policy and its Human Impact.(London and New York: Routledge, 2015
Rousseau, Fanon, and the Question of Method in Political Theory, a review of Jane Anna Gordon\u27s \u3cem\u3eCreolizing Political Theory: Reading Rousseau through Fanon\u3c/em\u3e
Putting in walls for the new classrooms at Parks. (May 1969) [Parks 1969 vol 02 folder, page 14
- …