Characterizing specification languages which admit initial semantics

AbstractThe paper proposes an axiomatic approach to specification languages, and introduces notions of reducibility and equivalence as tools for their study and comparison. Algebraic specification languages are characterized up to equivalence. They are shown to be limited in expressive power by implicational languages

Weak second order characterizations of various program verification systems

AbstractWe show the equivalence of Leivant's characterization of Floyd-Hoare Logic in weak second order logic (Leivant (1985)) with both Csirmaz's (1980) and Sain's (1985) characterizations of Floyd-Hoare logic in Nonstandard Logics of Programs. Our method allows us to spell out the precise role of the comprehension axiom in weak second order logic. We then prove similar results for other program verification systems (suggested by Burstall and Pnueli) and identify exactly the comprehension axioms corresponding to those systems

The parametrized complexity of knot polynomials

AbstractWe study the parametrized complexity of the knot (and link) polynomials known as Jones polynomials, Kauffman polynomials and HOMFLY polynomials. It is known that computing these polynomials is ♯P hard in general. We look for parameters of the combinatorial presentation of knots and links which make the computation of these polynomials to be fixed parameter tractable, i.e., in the complexity class FPT. If the link is explicitly presented as a closed braid, the number of its strands is known to be such a parameter. In a generalization thereof, if the link is explicitly presented as a combination of compositions and rotations of k-tangles the link is called k-algebraic, and its algebraicity k is such a parameter. The previously known proofs that, for this parameter, the link polynomials are in FPT uses the so called skein modules, and is algebraic in its nature. Furthermore, it is not clear how to find such an algebraic presentation from a given link diagram. We look at the treewidth of two combinatorial presentation of links: the crossing diagram and its shading diagram, a signed graph. We show that the treewidth of these two presentations and the algebraicity of links are all linearly related to each other. Furthermore, we characterize the k-algebraic links using the pathwidth of the crossing diagram. Using this, we can apply algorithms for testing fixed treewidth to find k-algebraic presentations in polynomial time. From this we can conclude that also treewidth and pathwidth are parameters of link diagrams for which the knot polynomials are FPT. For the Kauffman and Jones polynomials (but not for the HOMFLY polynomials) we get also a different proof for FPT via the corresponding result for signed Tutte polynomials

On the complexity of Generalized Chromatic Polynomials

J. Makowsky and B. Zilber (2004) showed that many variations of graph colorings, called CP-colorings in the sequel, give rise to graph polynomials. This is true in particular for harmonious colorings, convex colorings, mcct-colorings, and rainbow colorings, and many more. N. Linial (1986) showed that the chromatic polynomial �(G;X) is #P-hard to evaluate for all but three values X = 0, 1, 2, where evaluation is in P. This dichotomy includes evaluation at real or complex values, and has the further property that the set of points for which evaluation is in P is finite. We investigate how the complexity of evaluating univariate graph polynomials that arise from CPcolorings varies for different evaluation points. We show that for some CP-colorings (harmonious, convex) the complexity of evaluation follows a similar pattern to the chromatic polynomial. However, in other cases (proper edge colorings, mcct-colorings, H-free colorings) we could only obtain a dichotomy for evaluations at non-negative integer points. We also discuss some CP-colorings where we only have very partial results

Journeying through Dementia: the story of a 14 year design-led research enquiry

Consider a linear ordering equipped with a finite sequence of monadic predicates. If the ordering contains an interval of order type \omega or -\omega, and the monadic second-order theory of the combined structure is decidable, there exists a non-trivial expansion by a further monadic predicate that is still decidable.Comment: 18 page

Invariant Definability (Extended Abstract)

) J.A. Makowsky ? Department of Computer Science Technion---Israel Institute of Technology IL-32000 Haifa, Israel [email protected] Abstract. We define formally the notion of invariant definability in a logic L and study it systematically. We relate it to other notions of definability (implicit definability, \Delta-definability and definability with built-in relations) and establish connections between them. In descriptive complexity theory, invariant definability is mostly used with a linear order (or a successor relation) as the auxiliary relation. We formulate a conjecture which spells out the special role linear order plays in capturing complexity classes with logics and prove two special cases. 1 Introduction This paper initiates an analysis of the notion of invariant definability special cases of which have been used in various contexts of finite model theory and descriptive complexity theory. We assume the reader is familiar with the basics of complexity theory as given ..