Bulletin of the Section of Logic 2023-06-01T00:05:10+02:00 Andrzej Indrzejczak Open Journal Systems <div style="text-align: justify;"> <p>The <em>Bulletin of the Section of Logic</em> (<em>BSL</em>) is a quarterly peer-reviewed journal published with the support of the Lodz University Press. The <em>BSL</em> was founded in 1972 by Ryszard Wójcicki, Head of the Section of Logic of the Polish Academy of Sciences, then based in Wrocław, as a newsletter-journal designed for the exchange of scientific results among members of the Section with their national and international partners and colleagues. The first editor-in-chief of the <em>BSL</em> was Jan Zygmunt, who supervised the editorial process of the first six issues of the journal. In 1973 the role was taken over by Marek Tokarz. From 1975 to 2018 the journal was managed and edited by Grzegorz Malinowski. In 1992 the Department of Logic at the University of Łódź took over the publication from the Polish Academy of Sciences changing its policy into regular peer-reviewed journal. The aim of the <em>Bulletin</em> is to act as a forum for the prompt wide dissemination of original, significant results in logic through rapid publication. The <em>BSL</em> welcomes especially contributions dealing directly with logical calculi, their methodology, application and algebraic interpretations.</p> </div> Roughness of Filters in Equality Algebras 2023-06-01T00:05:10+02:00 Gholam Reza Rezaei Rajab Ali Borzooei Mona Aaly Kologani Young Bae Jun <p>Rough set theory is an excellent mathematical tool for the analysis of a vague description of actions in decision problems. Now, in this paper by considering the notion of an equality algebra, the notion of the lower and the upper approximations are introduced and some properties of them are given. Moreover, it is proved that the lower and the upper approximations define an interior operator and a closure operator, respectively. Also, using D-lower and D-upper approximation, conditions for a nonempty subset to be definable are provided and investigated that under which condition D-lower and D-upper approximation can be filter.</p> 2023-01-25T00:00:00+01:00 Copyright (c) 2020 On Homomorphism and Cartesian Products of Intuitionistic Fuzzy PMS-subalgebra of a PMS-algebra 2023-05-31T23:37:56+02:00 Beza Lamesgin Derseh Berhanu Assaye Alaba Yohannes Gedamu Wondifraw <p>In this paper, we introduce the notion of intuitionistic fuzzy PMS-subalgebras under homomorphism and Cartesian product and investigate several properties. We study the homomorphic image and inverse image of the intuitionistic fuzzy PMS-subalgebras of a PMS-algebra, which are also intuitionistic fuzzy PMS-subalgebras of a PMS-algebra, and find some other interesting results. Furthermore, we also prove that the Cartesian product of intuitionistic fuzzy PMS-subalgebras is again an intuitionistic fuzzy PMS-subalgebra and characterize it in terms of its level sets. Finally, we consider the strongest intuitionistic fuzzy PMS-relations on an intuitionistic fuzzy set in a PMS-algebra and demonstrate that an intuitionistic fuzzy PMS-relation on an intuitionistic fuzzy set in a PMS-algebra is an intuitionistic fuzzy PMS-subalgebra if and only if the corresponding intuitionistic fuzzy set in a PMS-algebra is an intuitionistic fuzzy PMS-subalgebra of a PMS-algebra.</p> 2023-04-21T00:00:00+02:00 Copyright (c) 2020 The Theory of an Arbitrary Higher \(\lambda\)-Model 2023-05-31T23:37:49+02:00 Daniel O. Martínez-Rivillas Ruy J. G. B. de Queiroz <p>One takes advantage of some basic properties of every homotopic \(\lambda\)-model (e.g. extensional Kan complex) to explore the higher \(\beta\eta\)-conversions, which would correspond to proofs of equality between terms of a theory of equality of any extensional Kan complex. Besides, Identity types based on computational paths are adapted to a type-free theory with higher \(\lambda\)-terms, whose equality rules would be contained in the theory of any \(\lambda\)-homotopic model.</p> 2023-04-25T00:00:00+02:00 Copyright (c) 2020 The Modelwise Interpolation Property of Semantic Logics 2023-05-31T23:37:52+02:00 Zalán Gyenis Zalán Molnár Övge Öztürk <p>In this paper we introduce the modelwise interpolation property of a logic that states that whenever \(\models\phi\to\psi\) holds for two formulas \(\phi\) and \(\psi\), then for every model \(\mathfrak{M}\) there is an interpolant formula \(\chi\) formulated in the intersection of the vocabularies of \(\phi\) and \(\psi\), such that \(\mathfrak{M}\models\phi\to\chi\) and \(\mathfrak{M}\models\chi\to\psi\), that is, the interpolant formula in Craig interpolation may vary from model to model. We compare the modelwise interpolation property with the standard Craig interpolation and with the local interpolation property by discussing examples, most notably the finite variable fragments of first order logic, and difference logic. As an application we connect the modelwise interpolation property with the local Beth definability, and we prove that the modelwise interpolation property of an algebraizable logic can be characterized by a weak form of the superamalgamation property of the class of algebras corresponding to the models of the logic.</p> 2023-04-21T00:00:00+02:00 Copyright (c) 2020 The Weak Variable Sharing Property 2023-01-12T17:26:40+01:00 Tore Fjetland Øgaard <div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>An algebraic type of structure is shown forth which is such that if it is a characteristic matrix for a logic, then that logic satisfies Meyer's weak variable sharing property. As a corollary, it is shown that <strong>RM</strong> and all its odd-valued extensions \(\mathbf{RM}_{2n\mathord{-}1}\) satisfy the weak variable sharing property. It is also shown that a proof to the effect that the "fuzzy" version of the relevant logic <strong>R</strong> satisfies the property is incorrect.</p> </div> </div> </div> 2023-04-21T00:00:00+02:00 Copyright (c) 2020