Talks and Poster Presentations (with Proceedings-Entry):

T. Eiter, A. Polleres:
"Transforming co-NP Checks to Answer Set Computation by Meta-Interpretation";
Talk: APPIA-GULP-PRODE 2003 - 2003 Joint Conference on Declarative Programming, Reggio Calabria, Italien; 2003-09-03 - 2003-09-05; in: "APPIA-GULP-PRODE 2003 - 2003 Joint Conference on Declarative Programming", F. Buccafurri (ed.); (2003), 410 - 421.

English abstract:
Answer set programming (ASP) with disjunction offers a powerful tool for declaratively representing and solving hard problems. Many NP-complete problems can be encoded in the answer set semantics of logic programs in a very concise and intuitive way, where the encoding reflects the typical ``guess and check" nature of NP problems: The property is encoded in a way such that polynomial size certificates for it correspond to stable models of a program. However, the problem-solving capacity of full disjunctive logic programs (DLPs) is beyond NP, and captures a class of problems at the second level of the polynomial hierarchy. While these problems also have a clear ``guess and check" structure, an encoding in a DLP reflecting it intuitively may sometimes be a non-obvious task, in particular if the ``check" itself is a co-NP-complete problem; usually, such problems are solved by interleaving separate guess and check programs, where the check is expressed by inconsistency of the check program. In this paper, we present general transformations of head-cycle free (extended) logic programs into stratified and positive (extended) disjunctive logic programs based on
meta-interpretation techniques. The answer sets of the original and
the transformed program are in simple correspondence, and, moreover,
inconsistency of the original program is indicated by a designated
answer set of the transformed program. This enables one to integrate
separate ``guess" and ``check" programs, which are often easy to
obtain, automatically into a single disjunctive logic program. Our
results complement recent results on meta-interpretation in ASP, and
extend methods and techniques for a declarative ``guess
and check" problem solving paradigm through ASP.

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