Designing Decidable Logics of Epistemology

We investigate the following “epistemic” extensions of (fragments of) first order logics: if phi is a formula, then box_i phi (i in I) is also a formula, where I is a fixed finite set. The intended meaning of box_i phi is “the i-th agent (ith participant of the model) knows phi”. The main result of the paper is Theorem 1: if L is such a fragment of first order logic whose consequence relation is weakly decidable, then the consequence relation of the epistemic extension of L remains weakly decidable, as well

Polyadic Algebras

This chapter surveys the development in the theory of polyadic algebras in the last decades

Some variants of Vaught’s conjecture from the perspective of algebraic logic

Vaught’s Conjecture states that if T is a complete first order theory in a countable language such that T has uncountably many pairwise non-isomorphic countably infinite models, then T has 2^ℵ_0 many pairwise non-isomorphic countably infinite models. Continuing investigations initiated in S´agi, we apply methods of algebraic logic to study some variants of Vaught’s conjecture. More concretely, let S be a σ-compact monoid of selfmaps of the the natural numbers. We prove, among other things, that if a complete first order theory T has at least ℵ1 many countable models that cannot be elementarily embedded into each other by elements of S, then, in fact, T has continuum many such models. We also study-related questions in the context of equality free logics and obtain similar results. Our proofs are based on the representation theory of cylindric and quasi-polyadic algebras (for details see Henkin, Monk and Tarski (cylindric Algebras Part 1 and Part 2)) and topological properties of the Stone spaces of these algebras

Heating causes non-linear microwave absorption anomaly in single wall carbon nanotubes

Microwave impedance measurements indicate a non-linear absorption anomaly in single wall carbon nanotubes at low temperatures (below $20$ K). We investigate the nature of the anomaly using a time resolved microwave impedance measurement technique. It proves that the anomaly has an extremely slow, a few hundred second long dynamics. This strongly suggests that the anomaly is not caused by an intrinsic electronic effect and that it is rather due to a slow heat exchange between the sample and the environment

The Role of COVID‐19 in Worsening the Debt Sustainability in Developing Economies

The SARS-CoV-2 coronavirus pandemic has raised public debt sustainability issues, especially for Heavily Indebted Poor Countries (HIPC). Developing countries with limited fiscal space have had to take on significant external debts to help deal with the negative effects of the pandemic. This has led to further increases in the debt levels of these countries, with the potential to trigger a debt default. Addressing these issues, this study uses a framework for fiscal policy and public debt sustainability analysis. The results confirm the impact of the SARS-CoV-2 coronavirus pandemic on the debt levels of Ghana and Kenya. This study recommends the creation of domestic fiscal buffers and fiscal space toward the attainment of long-term debt sustainability, contrary to the popular view of offering debt relief to these countries