Causal graphs are widely used in planning to capture the internal structure of planning instances. In the past, causal graphs have been exploited to generate hierarchical plans, to compute heuristics, and to identify classes of planning instances that are easy to solve. It is generally believed that planning is easier when the causal graph is acyclic. In this paper we show that this is not true...

There is a longstanding debate about how to appropriately model the combinability of affixes, especially English suffixes. One widely accepted principle is the notion of so-called selectional restrictions, i.e. grammatical requirements of particular affixes. For example, the suffix -ness can only combine with adjectival bases. Hay (2002) proposed a psycholinguistic approach to affix ordering no...

In this paper, we study the problem of finding all connected and Berge-acyclic sub-hypergraphs contained in an input hypergraph with potential applications to substructure mining from relational data, where Berge acyclicity is a generalization of a tree and one of the most retricted notion of acyclicity for hypergraphs (Fagin, J. ACM, Vol.30(3), pp.514–550, 1983). As main results, we present ef...

In a perimenopausal model of middle-aged rats, the astrocyte estrogen receptor-alpha (ERa): ER-beta (ERb) ratio increased with the onset of acyclicity (constant estrus, CE) in association with impaired neurotrophic responses to estradiol (E2). We report additional data on irregular cycling (IR) from this study of 9 month old perimenopausal subgroups. In particular, irregular cyclers (IR) also s...

The proliferation of contextualized knowledge in the Semantic Web (SW) has led to the popularity of knowledge formats such as quads in the SW community. A quad is an extension of an RDF triple with contextual information of the triple. In this paper, we study the problem of query answering over quads augmented with forall-existential bridge rules that enable interoperability of reasoning betwee...

Acyclicity of individual preferences is a minimal assumption in social choice theory. We replace that assumption by the direct assumption that preferences have maximal elements on a fixed agenda. We show that the core of a simple game is nonempty for all profiles of such preferences if and only if the number of alternatives in the agenda is less than the Nakamura number of the game. The same is...

Hierarchical decompositions are a useful tool for drawing large graphs. Such decompositions can be represented by means of a data structure called hierarchy tree. In this paper we introduce the notion of P-validity of hierarchy trees with respect to a given property P: this notion reflects the similarity between the topological structure of the original graph and of any high-level representatio...

It is known that a two-person game form g is Nash-solvable if and only if it is tight [12, 13]. We strengthen the concept of tightness as follows: game form is called totally tight if every its 2 × 2 subform is tight. (It is easy to show that in this case all, not only 2 × 2, subforms are tight.) We characterize totally tight game forms and derive from this characterization that they are tight,...

The complexity of evaluating conjunctive queries can depend significantly on the structure of the query. For example, it is well known that various notions of acyclicity can make the evaluation problem tractable. More generally, it seems that the complexity is connected to the “treelikeness” of the graph or hypergraph describing the query structure. In the lecture, we will review some of the no...