Compact Argumentation Frameworks

Abstract argumentation frameworks (AFs) are one of the most studied formalisms in AI. In this work, we introduce a certain subclass of AFs which we call compact. Given an extension-based semantics, the corresponding compact AFs are characterized by the feature that each argument of the AF occurs in at least one extension. This not only guarantees a certain notion of fairness; compact AFs are thus also minimal in the sense that no argument can be removed without changing the outcome. We address the following questions in the paper: (1) How are the classes of compact AFs related for different semantics? (2) Under which circumstances can AFs be transformed into equivalent compact ones? (3) Finally, we show that compact AFs are indeed a non-trivial subclass, since the verification problem remains coNP-hard for certain semantics.Comment: Contribution to the 15th International Workshop on Non-Monotonic Reasoning, 2014, Vienn

Welfare maximization with friends-of-friends network externalities

Online social networks allow the collection of large amounts of data about the influence between users connected by a friendship-like relationship. When distributing items among agents forming a social network, this information allows us to exploit network externalities that each agent receives from his neighbors that get the same item. In this paper we consider Friends-of-Friends (2-hop) network externalities, i.e., externalities that not only depend on the neighbors that get the same item but also on neighbors of neighbors. For these externalities we study a setting where multiple different items are assigned to unit-demand agents. Specifically, we study the problem of welfare maximization under different types of externality functions. Let n be the number of agents and m be the number of items. Our contributions are the following: (1) We show that welfare maximization is APX-hard; we show that even for step functions with 2-hop (and also with 1-hop) externalities it is NP-hard to approximate social welfare better than (1-1/e). (2) On the positive side we present (i) an O(sqrt n)-approximation algorithm for general concave externality functions, (ii) an O(\log m)-approximation algorithm for linear externality functions, and (iii) an (1-1/e)\frac{1}{6}-approximation algorithm for 2-hop step function externalities. We also improve the result from [6] for 1-hop step function externalities by giving a (1-1/e)/2-approximation algorithm

Improved set-based symbolic algorithms for parity games

Graph games with omega-regular winning conditions provide a mathematical framework to analyze a wide range of problems in the analysis of reactive systems and programs (such as the synthesis of reactive systems, program repair, and the verification of branching time properties). Parity conditions are canonical forms to specify omega-regular winning conditions. Graph games with parity conditions are equivalent to mu-calculus model checking, and thus a very important algorithmic problem. Symbolic algorithms are of great significance because they provide scalable algorithms for the analysis of large finite-state systems, as well as algorithms for the analysis of infinite-state systems with finite quotient. A set-based symbolic algorithm uses the basic set operations and the one-step predecessor operators. We consider graph games with n vertices and parity conditions with c priorities (equivalently, a mu-calculus formula with c alternations of least and greatest fixed points). While many explicit algorithms exist for graph games with parity conditions, for set-based symbolic algorithms there are only two algorithms (notice that we use space to refer to the number of sets stored by a symbolic algorithm): (a) the basic algorithm that requires O(n^c) symbolic operations and linear space; and (b) an improved algorithm that requires O(n^{c/2+1}) symbolic operations but also O(n^{c/2+1}) space (i.e., exponential space). In this work we present two set-based symbolic algorithms for parity games: (a) our first algorithm requires O(n^{c/2+1}) symbolic operations and only requires linear space; and (b) developing on our first algorithm, we present an algorithm that requires O(n^{c/3+1}) symbolic operations and only linear space. We also present the first linear space set-based symbolic algorithm for parity games that requires at most a sub-exponential number of symbolic operations

25 Concurs internacional de cant Francesc Viñas, concert final

Programa del Concert final de la 25ena edició del Concurs internacional de cant Francesc Viñas que va tenir lloc al Gran Teatre del Liceu el 15 de novembre de 1987. Els participants van interpretar fragments de Les noces de Figaro i La flauta màgica de Mozart, la Passió segons Sant Mateu de Bach, Un ballo in maschera, Rigoletto, Don Carlo i Ernani de Verdi, Il barbiere di Siviglia de Rossini, Mefistofele d'A. Boito, Carmen de Bizet, Rusalka de Dvorak, La Wally d'A. Catalani i Lucia di Lammermoor de Donizetti. L'Orquestra del Gran Teatre del Liceu va actuar sota la direcció de M. Gibson i al piano hi va haver À. Sole

Algorithms and conditional lower bounds for planning problems

We consider planning problems for graphs, Markov decision processes (MDPs), and games on graphs. While graphs represent the most basic planning model, MDPs represent interaction with nature and games on graphs represent interaction with an adversarial environment. We consider two planning problems where there are k different target sets, and the problems are as follows: (a) the coverage problem asks whether there is a plan for each individual target set; and (b) the sequential target reachability problem asks whether the targets can be reached in sequence. For the coverage problem, we present a linear-time algorithm for graphs, and quadratic conditional lower bound for MDPs and games on graphs. For the sequential target problem, we present a linear-time algorithm for graphs, a sub-quadratic algorithm for MDPs, and a quadratic conditional lower bound for games on graphs. Our results with conditional lower bounds establish (i) model-separation results showing that for the coverage problem MDPs and games on graphs are harder than graphs and for the sequential reachability problem games on graphs are harder than MDPs and graphs; and (ii) objective-separation results showing that for MDPs the coverage problem is harder than the sequential target problem

Cinco grandes conciertos

Direcció Artística Napoleone AnnovazziEmpresa José F. ArquerIntèrprets : Carmen Pérez Durias, Lolita Torrento, Pura Gómez, Rosario Gómez, Luis Corbella, Christian Ferrás, Narciso YepesOrquesta sinfónica del Gran Teatro del Liceo; directors Jascha Horenstein, Henry Swoboda, Eduard Toldrà, Philip WestPrograma de la temporada de quaresma del 1952, del 6 al 16 de març, que inclou: Simfonia número 7 de Ludwig van Beethoven; Adagio e Allegro de Luigi Boccherini; Primera Simfonia i Sonata en Fa Major de Johannes Brahms; Concert per a violoncel i orquestra d'Antonin Dvórak; Papillon opus 77 de Gabriel Fauré; Música de baile d'André Gretry; Capriccio opus 8 i Nobilissima Visione de Paul Hindemith; obertura de Le Nozze de Figaro, Simfonia Júpiter en Do, Serenata Nocturna i Concert per a dos pianos i orquetra de Wolfgang Amadeus Mozart; Simfonia de Pergolesi; Obertura de Manfred de Robert Schumann; obertura de Prodaná Nevesta de Bedrich Smetana; Canción de El cisne negro d'Heitor Villalobos; Die Meistersinger von Nuremberg de Richard Wagner; Tarantella opus 23 d'Alfredo Carlo Piatti; Suite italiana d'Igor Stravinsky; Quarta simfonia i Variacions d'un tema rococó de Piotr Ilitx Txaikowski; Homenaje a la Tempranica, Concierto de Aranjuez per a guitarra i orquestra, Cansoneta per a violí i orquestra de corda, Concert per a violí i orquestra, Quatre madrigals amatoris per a soprano i orquestra i Ausencias de Dulcinea, de Joaquín Rodrig