Decidability of the Admissibility Problem for Inference Rules in Some <Emphasis Type="Italic">S</Emphasis>5<Subscript>t</Subscript>-Logics

We examine some many-modal logics extending S5_t, t ∈ N, for decidability w.r.t. admissibility of inference rules, and for the logics in question, we prove an algorithmic criterion determining whether the inference rules in them are admissible.__________Translated from Algebra i Logika, Vol. 44, No. 4, pp. 438–458, July–August, 2005.     

An Inheritance Criterion for the Admissible Inference Rules of K4

We give a criterion for inheritance of the admissible inference rules of the modal logic K4 by the finitely approximable modal logics extending K4. We give a negative solution to the question of inheritance of the admissible rules of K4 by tabular logics. We exhibit a series of examples of modal logics which inherit or fail to inherit the admissible inference rules of K4.     

Bases of admissible rules for <Emphasis Type="Italic">K</Emphasis>-saturated logics

Admissible inference rules for table modal and superintuitionistic logics are investigated. K-saturated logics are defined semantically. Such logics are proved to have finite bases for admissible inference rules in finitely many variables. __________ Translated from Algebra i Logika, Vol. 47, No. 6, pp. 750–761, November–December, 2008.     

An explicit basis for the admissible inference rules in the Gödel-Löb logic <Emphasis Type="Italic">GL</Emphasis>

We describe an explicit basis for the admissible inference rules in the Gödel-Löb logic. The basis consists of a sequence of inference rules in infinitely many variables. Inference rules in the reduced form play an important role in this study. Alongside a basis for the admissible rules we obtain a basis for the quasi-identities of the countable rank free algebra in the Gödel-Löb logic.     

An explicit basis for admissible inference rules in table modal logics of width 2

We construct an explicit finite basis for admissible inference rules in an arbitrary modal logic of width 2 extending the logic Grz. Translated from Algebra i Logika, Vol. 48, No. 1, pp. 122–148, January–February, 2009.     

Definability in Normal Extensions of S4

A projective Beth property, PB2, in normal modal logics extending S4 is studied. A convenient criterion is furnished for PB2 to be valid in a larger family of extensions of K4. All locally tabular extensions of the Grzegorczyk logic with PB2 are described. Superintuitionistic logics with the projective Beth property that have no modal companions with this property are found.     

Construction of an Explicit Basis for Rules Admissible in Modal System S4

We find an explicit basis for all admissible rules of the modal logic S4. Our basis consists of an infinite sequence of rules which have compact and simple, readable form and depend on increasing set of variables. This gives a basis for all quasi‐identities valid in the free modal algebra ℱ_S4(ω) of countable rank.     

An explicit basis for the admissible inference rules of the modal logics extending <Emphasis Type="Italic">S</Emphasis>4.1 And <Emphasis Type="Italic">Grz</Emphasis>

We study bases for the admissible inference rules in a broad class of modal logics. We construct an explicit basis for all admissible rules in the logics S4.1, Grz, and their extensions whose number is at least countable. The resulting basis consists of an infinite sequence of rules in a concise and simple form. In the case of a logic of finite width a basis for all admissible rules consists of a finite sequence of rules.     

A Basis in Semi‐Reduced Form for the Admissible Rules of the Intuitionistic Logic IPC

We study the problem of finding a basis for all rules admissible in the intuitionistic propositional logic IPC. The main result is Theorem 3.1 which gives a basis consisting of all rules in semi‐reduced form satisfying certain specific additional requirements. Using developed technique we also find a basis for rules admissible in the logic of excluded middle law KC.     

The Resolution Method for One Reducible Class of Formulas of the First-Order Modal Logic S4

In the paper, we describe a resolution method for the family of the formulas of the form *ⁱ**(L ₁ L _s ), where i = 0 1 and L _j are modal literals. Negations here stand directly before classical atomic formulas, the formulas may contain constants. We also present the absorption tactics for a set of such formulas.__________Translated from Lietuvos Matematikos Rinkinys, Vol. 44, No. 4, pp. 481–492, October–December, 2004.