On Modal μ-Calculus and Non-Well-Founded Set Theory

A finitary characterization for non-well-founded sets with finite transitive closure is established in terms of a greatest fixpoint formula of the modal -calculus. This generalizes the standard result in the literature where a finitary modal characterization is provided only for wellfounded sets with finite transitive closure. The proof relies on the concept of automaton, leading then to new interlinks between automata theory and non-well-founded sets.     

Categorical Abstract Algebraic Logic Metalogical Properties

Metalogical properties that have traditionally been studied in the deductive system context (see, e.g., [21]) and transferred later to the institution context [33], are here formulated in the -institution context. Preservation under deductive equivalence of -institutions is investigated. If a property is known to hold in all algebraic -institutions and is preserved under deductive equivalence, then it follows that it holds in all algebraizable -institutions in the sense of [36].     

Every Finitely Reducible Logic has the Finite Model Property with Respect to the Class of ♦-Formulae

In this paper a unified framework for dealing with a broad family of propositional multimodal logics is developed. The key tools for presentation of the logics are the notions of closure relation operation and monotonous relation operation. The two classes of logics: FiRe-logics (finitely reducible logics) and LaFiRe-logics (FiRe-logics with local agreement of accessibility relations) are introduced within the proposed framework. Further classes of logics can be handled indirectly by means of suitable translations. It is shown that the logics from these classes have the finite model property with respect to the class of -formulae, i.e. each -formula has a -model iff it has a finite -model. Roughly speaking, a -formula is logically equivalent to a formula in negative normal form without occurrences of modal operators with necessity force. In the proof we introduce a substantial modification of Claudio Cerrato's filtration technique that has been originally designed for graded modal logics. The main core of the proof consists in building adequate restrictions of models while preserving the semantics of the operators used to build terms indexing the modal operators.     

Proof-Theoretic Modal PA-Completeness III: The Syntactic Proof

This paper is the final part of the syntactic demonstration of the Arithmetical Completeness of the modal system G; in the preceding parts [9] and [10] the tools for the proof were defined, in particular the notion of syntactic countermodel. Our strategy is: PA-completeness of G as a search for interpretations which force the distance between G and a GL-LIN-theorem to zero. If the GL-LIN-theorem S is not a G-theorem, we construct a formula H expressing the non G-provability of S, so that ⊢_GL-LIN ∼ H and so that a canonical proof T of ∼ H in GL-LIN is a syntactic countermodel for S with respect to G, which has the height θ(T) equal to the distance d(S, G) of S from G. Then we define the interpretation ξ of S which represents the proof-tree T in PA. By induction on θ(T), we prove that ⊢_PA S^ξ and d(S, G) > 0 imply the inconsistency of PA. This revised version was published online in June 2006 with corrections to the Cover Date.     

Predicate Logics on Display

The paper provides a uniform Gentzen-style proof-theoretic framework for various subsystems of classical predicate logic. In particular, predicate logics obtained by adopting van Behthem's modal perspective on first-order logic are considered. The Gentzen systems for these logics augment Belnap's display logic by introduction rules for the existential and the universal quantifier. These rules for x and x are analogous to the display introduction rules for the modal operators and and do not themselves allow the Barcan formula or its converse to be derived. En route from the minimal modal predicate logic to full first-order logic, axiomatic extensions are captured by purely structural sequent rules.     

On Quantitative and Qualitative Parsimony

The distinction between quantitative and qualitative parsimony is supposed to allow David Lewis to dismiss one of the charges against his modal realism: that is, the charge of bloated ontology. The aim of this paper is to undermine Lewis's response to this objection. In order to do this, a distinction between multipliable and nonmultipliable objects is introduced. Based on this it is argued that the acceptance of Lewis's response requires one to believe in modal realism in the first place—that is, one has to believe in the view that the existence of nonactual spatiotemporal worlds does not affect the quality of the ontological commitment. Although the paper focuses on the problem of the metaphysics of possible worlds, this should be regarded merely as a case study. Accordingly, the results of this analysis should find applications in other metaphysical debates as well.     

Advanced Brief Strategic Therapy: An overview of interventions with eating disorders to exemplify how theory and practice work

This paper aims at introducing some of the central aspects of the evolution that brief strategic therapy has undergone at the Centro di Terapia Strategica of Arezzo, Italy, towards advanced therapeutic strategies which differ from the original Palo Alto model. (Fisch, Weakland, &; Segal, 1982; Watzlawick, 1978 Watzlawick, P. 1978. The language of change: Elements of therapeutic communication, New York: Basic Books.  [Google Scholar]; Watzlawick, Beavin, &; Jackson, 1967; Watzlawick, Weakland, &; Fisch, 1974). We will focus on how the concept of self-deception is central to the formation and the persistence of psychological disorders; and how the usage of non-ordinary logics and the understanding of the individual's perceptive-reactive system are of key importance in unravelling such disorders, allowing the therapist to guide the patient towards an efficacious and efficient solution. Rather than attempting to describe and enlist the theoretical corpus that underlies brief strategic therapy, we have chosen to exemplify some focal concepts that connect theory to practice, and vice versa, by presenting the outline of some therapeutic protocols devised for solving eating disorders which can be specifically tailored for each individual patient.