We consider extensions of xed-point logic by means of generalized quantiiers in the context of descriptive complexity. By the well-known theorem of Immerman and Vardi, xed-point logic captures PTime over linearly ordered structures. It fails, however , to express even most fundamental structural properties, like simple cardinality properties, in the absence of order. In the present investigatio...

The classical logical antinomy known as Richard-Berry paradox is combined with plausible assumptions about the size i.e. the descriptional complexity, of Turing machines formalizing certain sentences, to show that formalization of language leads to contradiction.

We quickly review labelled Markov processes (LMP) and provide a counterexample showing that in general measurable spaces, event bisimilarity and state bisimilarity differ in LMP. This shows that the logic in Desharnais [3] does not characterize state bisimulation in non-analytic measurable spaces. Furthermore we show that, under current foundations of Mathematics, such logical characterization ...

The paper examines the concept of hairpin-free words motivated from the biocomputing and bioinformatics fields. Hairpin (-free) DNA structures have numerous applications to DNA computing and molecular genetics in general. A word is called hairpin-free if it cannot be written in the form xvyθ(v)z, with certain additional conditions, for an involution θ (a function θ with the property that θ equa...

We propose a framework for modelling and solving search problems using logic, and describe a project whose goal is to produce practically effective, general purpose tools for representing and solving search problems based on this framework. The mathematical foundation lies in the areas of finite model theory and descriptive complexity, which provide us with many classical results, as well as po...

A didactical survey of the foundations of Algorithmic Information Theory. These notes are short on motivation, history and background but introduce some of the main techniques and concepts of the field. The “manuscript” has been evolving over the years. Please, look at “Version history” below to see what has changed when.

Model theory is a branch of mathematical logic that investigates the logical properties of mathematical structures. It has been quite successfully applied to computational complexity resulting in an area of research called descriptive complexity theory. Descriptive complexity is essentially a syntactical characterization of complexity classes using logical formalisms. However, there are still m...

The lattice E of c.e. sets is a popular object of study in Computability Theory [So87]. A principal fact about this lattice is the undecidability of its first-order theory Th(E). Moreover, Th(E) is known [HN98] to be m-equivalent to the first-order arithmetic Th(N) where N := (ω; +,×). The lattice E may be considered as the lattice of effectively open subsets of the discrete topological space ω...

In this paper, we will prove the inevitable non-uniformity of two constructions from combinatorial group theory related to the word problem for finitely generated groups and the Higman-Neumann-Neumann Embedding Theorem.

Three Notions of Classification Consider your favorite class ofmathematical structures, be it groups, modules, measure-preserving transformations, C-algebras, Lie groups, smooth manifolds, or something completely different. With some probability, the classification problem for these objects, that is, the problem of determining the structures up to some relevant notion of isomorphism, is, or has...