We use a new version of the Definability Theorem of Beth in order to unify classical Theorems of Yuri Matiyasevich and Jan Denef in one structural statement. We give similar forms for other important definability results from Arithmetic and Number Theory. A.M.S. Classification: Primary 03B99; Secondary 11D99.

Rough set theory is an effective tool for data mining. According to the theory, a concept is definable if it can be written as a Boolean combination of equivalence classes induced from classification attributes. On the other hand, definability in logic has been explicated by Beth’s theorem. In this paper, we propose two data representation formalisms, called first-order data logic (FODL) and at...

A class of Kripke frames is called modally definable if there is a set of modal formulas such that the class consists exactly of frames on which every formula from that set is valid, i. e. globally true under any valuation. Here, existential definability of Kripke frame classes is defined analogously, by demanding that each formula from a defining set is satisfiable under any valuation. This is...

The question of whether knowledge is definable in terms of belief, which has played an important role in epistemology for the last fifty years, is studied here in the framework of epistemic and doxastic logics. Three notions of definability are considered: explicit definability, implicit definability, and reducibility, where explicit definability is equivalent to the combination of implicit def...

The question of whether knowledge is definable in terms of belief, which has played an important role in epistemology for the last fifty years, is studied here in the framework of epistemic and doxastic logics. Three notions of definability are considered: explicit definability, implicit definability, and reducibility, where explicit definability is equivalent to the combination of implicit def...

In this paper we study the expressive power and definability for (extended) modal languages interpreted on topological spaces. We provide topological analogues of the van Benthem characterization theorem and the Goldblatt-Thomason definability theorem in terms of the well established first-order topological language Lt.

We introduce the definability strength of combinatorial principles. In terms of definability strength, a combinatorial principle is strong if solving a corresponding combinatorial problem could help in simplifying the definition of a definable set. We prove that some consequences of Ramsey’s Theorem for colorings of pairs could help in simplifying the definitions of some Δ2 sets, while some oth...

Let T be a first order theory formulated in the language L and P a new relation symbol not in L. Let φ(P ) be an L ∪ {P}-sentence. Let us say that φ(P ) defines P implicitly in T if T proves φ(P ) ∧ φ(P ) → ∀x(P (x) ↔ P (x)). Beth’s definability theorem states that if φ(P ) defines P implicitlly in T then P (x) is equivalent to an L-formula. However, if we consider implicit definability in a gi...

In this paper we develop definability theory in such a way that we allow to define new elements also, not only new relations on already existing elements. This is in harmony with our everyday mathematical practice, for example we define new entities when we define a geometry over a field. We will see that, in many respects, defining new elements is more harmonious in many-sorted logic than in o...