A History of Until

Until is a notoriously difficult temporal operator as it is both existential and universal at the same time: A until B holds at the current time instant w iff either B holds at w or there exists a time instant w' in the future at which B holds and such that A holds in all the time instants between the current one and w'. This "ambivalent" nature poses a significant challenge when attempting to give deduction rules for until. In this paper, in contrast, we make explicit this duality of until to provide well-behaved natural deduction rules for linear-time logics by introducing a new temporal operator that allows us to formalize the "history" of until, i.e., the "internal" universal quantification over the time instants between the current one and w'. This approach provides the basis for formalizing deduction systems for temporal logics endowed with the until operator. For concreteness, we give here a labeled natural deduction system for a linear-time logic endowed with the new operator and show that, via a proper translation, such a system is also sound and complete with respect to the linear temporal logic LTL with until.Comment: 24 pages, full version of paper at Methods for Modalities 2009 (M4M-6

Regional Business Cycles and National Economic Borders - What are the Effects of Trade in Developing Countries?

Does trade lead to increased cross-country regional business cycle synchronization and reduced national economic borders? The theory does not really provide an unambiguous answer. Our paper addresses empirically this question using Argentina and Brazil as case studies of developing countries. These countries liberalized unilaterally trade since the mid-1980s and also established MERCOSUR (a regional integration agreement with Paraguay and Uruguay) in 1991. As a consequence, the intensity of trade between Argentina and Brazil rose significantly. The answer to the initial question is no. The increase in bilateral trade between Argentina and Brazil did not translate into significantly more synchronized regional business cycles. Using Gross Provincial Product for Argentina and Gross State Product for Brazil for the period 1961 to 2000, we find that within-country regional business cycle synchronization is substantially larger than cross-country regional business cycle synchronization. Moreover, this difference has increased over time. These results are mainly driven by Argentina’s behavior and hold even after controlling for factors such as distance, size, sectoral specialization, and the degree of regional fiscal policy coordination. The empirical evidence based on Brazilian states and Argentina as a whole suggests that the higher level of trade among regions within a country is an important factor to that accounts for the observed border effect. In the case of Argentina additional factors such as monetary and exchange rate policies and large country-specific shocks have also played a significant role.

The traditional, the innovative, the ephemeral: conception, realization, intervention in contemporary art

The traditional, the innovative, the ephemeral: conception, realization, intervention in contemporary art. One must consider the traditional, the innovative and also the ephemeral related to the artistic intentions and thus to the interventions on works of contemporary art, for which the concepts of originality and authenticity do not always correspond. The Brandian vision and point of view do not completely resolve the problematics relative to restoration and conservation: artists realize their artifacts with the intention of undermining tradition or, however, of interpreting it in an unusual way. There are, therefore, cases when a diagnostic-analytical and conservative intervention is possible correspondently to the different and numerous typologies of the materials (poor, plastic, industrial) and techniques (collage, enamel on rubber foam, paint on textile or plastic, neon). A vocation for the ephemeral can be transformed into the adoption of deteriorated materials or into the realization of works of conceptual art and net-art. Some case studies are treated in the comparison of art works of different age. The solutions to the aforementioned problematics are offered and the importance of the involvement of the historical-technical experts, authors and manufacturers of the materials used in the artifacts is highlighted. Finally the procedure of intervention cannot be the same for all works of contemporary art. One must employ a methodology based on the critical study, not only of the materials used but also of the philosophy and creative conceptual intentions of the artist