The complexity of theorem proving in circumscription and minimal entailment

We provide the first comprehensive proof-complexity analysis of different proof systems for propositional circumscription. In particular, we investigate two sequent-style calculi: MLK defined by Olivetti [28] and CIRC introduced by Bonatti and Olivetti [8], and the tableaux calculus NTAB suggested by Niemelä [26]. In our analysis we obtain exponential lower bounds for the proof size in NTAB and CIRC and show a polynomial simulation of CIRC by MLK. This yields a chain NTAB < CIRC < MLK of proof systems for circumscription of strictly increasing strength with respect to lengths of proofs

Perspectives in deductive databases

AbstractI discuss my experiences, some of the work that I have done, and related work that influenced me, concerning deductive databases, over the last 30 years. I divide this time period into three roughly equal parts: 1957–1968, 1969–1978, 1979–present. For the first I describe how my interest started in deductive databases in 1957, at a time when the field of databases did not even exist. I describe work in the beginning years, leading to the start of deductive databases about 1968 with the work of Cordell Green and Bertram Raphael. The second period saw a great deal of work in theorem providing as well as the introduction of logic programming. The existence and importance of deductive databases as a formal and viable discipline received its impetus at a workshop held in Toulouse, France, in 1977, which culminated in the book Logic and Data Bases. The relationship of deductive databases and logic programming was recognized at that time. During the third period we have seen formal theories of databases come about as an outgrowth of that work, and the recognition that artificial intelligence and deductive databases are closely related, at least through the so-called expert database systems. I expect that the relationships between techniques from formal logic, databases, logic programming, and artificial intelligence will continue to be explored and the field of deductive databases will become a more prominent area of computer science in coming years

Stability of career aspirations: a test of Gottfredson\u27s theory of circumscription and compromise

Gottfredson\u27s (1981) developmental theory of career choices was evaluated using longitudinal data. This study builds on previous research into Gottfredson\u27s model by addressing methodological issues in the confounding of sex type, prestige, and interest measures when measuring expressed career choices by statistically controlling for the inter-relations among these variables in the analyses. Participants were 2,353 women enrolled at the Seven College Conference Schools and 321 men enrolled at Harvard and Vassar. Expressed career preferences were coded for sex type, prestige, and the Things/People and Data/Ideas interest dimension. Stability of expressed career choices over a one year period and discrepancies between current career choices and idealized aspirations were analyzed using partial correlation analyses to control for the non-independence of the constructs. Gottfredson\u27s (1981) theory was not supported for either men or women, because prestige and the Things/People dimension of interest were found to be more stable than sex type. Implications for re-conceptualizing Gottfredson\u27s theory are discussed, along with implications for research and practice

Applications of Intuitionistic Logic in Answer Set Programming

We present some applications of intermediate logics in the field of Answer Set Programming (ASP). A brief, but comprehensive introduction to the answer set semantics, intuitionistic and other intermediate logics is given. Some equivalence notions and their applications are discussed. Some results on intermediate logics are shown, and applied later to prove properties of answer sets. A characterization of answer sets for logic programs with nested expressions is provided in terms of intuitionistic provability, generalizing a recent result given by Pearce. It is known that the answer set semantics for logic programs with nested expressions may select non-minimal models. Minimal models can be very important in some applications, therefore we studied them; in particular we obtain a characterization, in terms of intuitionistic logic, of answer sets which are also minimal models. We show that the logic G3 characterizes the notion of strong equivalence between programs under the semantic induced by these models. Finally we discuss possible applications and consequences of our results. They clearly state interesting links between ASP and intermediate logics, which might bring research in these two areas together.Comment: 30 pages, Under consideration for publication in Theory and Practice of Logic Programmin

Conservation of Lactuca watsoniana Trelease, an Azorean priority species : phylogenetics, population genetics and propagation

Tese de Doutoramento, Biologia, 28 de maio de 2018, Universidade dos Açores.Lactuca watsoniana Trel., é uma herbácea perene, endémica do Arquipélago dos Açores. Localmente denominada de “Alfacinha”, pode ser encontrada em quatro das nove ilhas do Arquipélago dos Açores (Faial, Pico, Terceira e São Miguel), estando possivelmente extinta da ilha de São Jorge. O tamanho total estimado das populações é de 500 a 2000 indivíduos, mas observações recentes no campo indicam que poderão ser menos de 500 indivíduos. Considerada como taxon prioritário na Directiva Habitats (Annex B-II) bem como na Convenção de Berna em termos de conservação e está listada como ameaçada (EN B2ab (i, ii, iii); C2a(i)) na Lista Vermelha da IUCN 2017. Atualmente, a Lactuca watsoniana encontra-se restrita a zonas húmidas, ravinas profundas e estreitas, crateras zonas declivosas, prados naturais de Festuca, matos de Erica e florestas de Juniperus entre 600-800 m. Está ameaçada por perda e degradação de habitat, resultante de expansão dos pastos, invasão por espécies exóticas, introdução de herbívoros e distúrbio de áreas sensíveis por turistas e locais. Neste trabalho investigaram-se os seguintes tópicos: i) propagação vegetativa por sementes; ii) genética de populações; e iii) filogenética e filogeografia. Foi estabelecido um protocolo eficaz e exequível para propagação por via seminal, germinando as sementes com 0.1 mg l-1 GA3, ethephon, e um filtro de luz vermelha e um regime de temperatura alterna de 15/10°C, com um fotoperíodo de 12 horas. Este protocolo permitiu a produção de centenas de plântulas viáveis que foram replantadas na população de origem. Dada a necessidade de proceder ao reforço das populações naturais em algumas ilhas, pretendeu-se definir se existiam riscos de contaminação genética resultante da troca de material entre as diferentes ilhas, para isso estudou-se a estrutura e variabilidade genética das populações, usando 8 microssatélites nucleares, desenvolvidos especificamente para a L. watsoniana. Os resultados mostraram uma clara separação entre as várias ilhas dos Açores, estando a maior variação genética dentro das populações (55.0%), mas com níveis relativamente altos de variação entre os clusters (27.3%). Evidenciando um grau de diferenciação entre as populações elevado e fluxo genético com valores inferiores a 1, bem como a existência de isolamento e barreiras geográficas. De modo a clarificar a posição taxonómica da L. watsoniana, nomeadamente em relação a espécies próximas da Europa, Norte da América e de outros Arquipélagos da Macaronésia (Canárias), recorremos a marcadores moleculares nucleares (ITS) e quatro do cloroplasto. Na análise das sequências combinadas de ITS e do cloroplasto (Parsimónia, Máxima verosimilhança e Inferência Baeysiana) o taxon dos Açores, mostrou a existência de um padrão filogeográfico através do arquipélago, com a presença de 5 haplótipos distintos para a L. watsoniana, quatro endémicos em apenas uma ilha (Faial, Pico, Terceira e São Miguel) e um haplótipo com informação genética partilhada do Faial e Pico, bem como uma relação filogenética, bem suportada, com as Lactuca Norte Americanas.ABSTRACT: Lactuca watsoniana Trel., is a perennial herb, endemic to the Azores archipelago. Locally called "Alfacinha", the species is restricted to only four of the nine islands of the archipelago (São Miguel, Terceira, Pico and Faial) and is possibly extinct in São Jorge Island. Estimates of its total population size are 500 to 2,000 individuals, but recent field observations indicate that it can be fewer than 500 individuals. It is therefore considered a priority species for conservation and was listed as endangered on the IUCN Red List 2017. Furthermore, it was included in Annex II of the EC Habitats Directive and is protected under the Berne Convention. Lactuca watsoniana is currently restricted to the steep slopes of craters and ravines in temperate juniper rain forest between 600-800 m of altitude. The species is threatened by habitat loss and degradation resulting from changes in land use, namely expansion of pasture, invasion by exotic species, consumption by introduced herbivores and disturbance of sensitive areas by tourists and locals. In this thesis, we investigated the following topics: i) seed propagation; ii) population genetics; and iii) phylogenetics and phylogeography. We established and efficient and feasible seed propagation protocol by germinating the seeds germinate seeds with 0.1 mg l-1 GA3, ethephon, a red-light filter and a temperature regime of 15/10°C, and 12 hours’ photoperiod. This protocol allowed producing hundreds of viable seedlings that were reintroduced in the source population. Given the need to reinforce natural populations in some of the islands, we aimed to find out if any outbreeding risks existed, resulting from material exchanges between the different islands. For that, we studied the genetic structure and variability of the populations, using eight nuclear microsatellites, developed specifically, for Lactuca watsoniana. Our findings showed a clear separation among the islands, with the largest proportion of genetic variation found within populations (55.0%) but with relatively high levels of genetic variation both among clusters (27.3%). Furthermore, a high variability between the populations, a gene flow value below one, and the presence of geographical isolation and barriers were estimated. In order to clarify the taxonomic position of L. watsoniana, namely the phylogeographic and phylogenetic relationship with the morphologically similar species from Europe, North America and the geographically close taxa from the Canary Islands, we used one nuclear region (ITS) and four chloroplast markers. Parsimony, Maximum likelyhood and Bayesian Inference analyses were conducted and revealed a strongly supported monophyletic Lactuca clade, and a clear separation of Macaronesian endemic Lactuca in sister clades. Lactuca watsoniana, endemic to Azores, showed a phylogeographic pattern across the archipelago, with the presence of five different haplotypes for L. watsoniana: four single island endemics (Faial, Pico, Terceira e São Miguel) and one occurring on both Faial and Pico and a strongly supported phylogenetic relationship with North America Lactuca.Fundo Regional da Ciência pelo financiamento da Bolsa de Doutoramento (M3.1.2/F/032/2011 e FEDER funds through the Operational Programme for Competitiveness Factors - COMPETE

Negation-as-failure considered harmful

In logic programs, negation-as-failure has been used both for representing negative information and for providing default nonmonotonic inference. In this paper we argue that this twofold role is not only unnecessary for the expressiveness of the language, but it also plays against declarative programming, especially if further negation symbols such as strong negation are also available. We therefore propose a new logic programming approach in which negation and default inference are independent, orthogonal concepts. Semantical characterization of this approach is given in the style of answer sets, but other approaches are also possible. Finally, we compare them with the semantics for logic programs with two kinds of negation.Red de Universidades con Carreras en Informática (RedUNCI