Finite bases with respect to admissibility for modal logics of width 2

It is proved that every finitely approximable and residually finite modal logic of depth 2 over K4 has a finite basis of admissible inference rules. This, in particular, implies that every finitely approximable residually finite modal logic of depth at most 2 is finitely based w.r.t. admissibility. (Among logics in a larger depth or width, there are logics which do not have a finite, or even independent, basis of admissible rules of inference.) Translated fromAlgebra i Logika, Vol. 38, No. 4, pp. 436–455, July–August 1999.     

Densities in large permutations and parameter testing

A classical theorem of Erdős, Lovász and Spencer asserts that the densities of connected subgraphs in large graphs are independent. We prove an analogue of this theorem for permutations and we then apply the methods used in the proof to give an example of a finitely approximable permutation parameter that is not finitely forcible. The latter answers a question posed by two of the authors and Moreira and Sampaio.     

Profinite Heyting Algebras

For a Heyting algebra A, we show that the following conditions are equivalent: (i) A is profinite; (ii) A is finitely approximable, complete, and completely join-prime generated; (iii) A is isomorphic to the Heyting algebra Up(X) of upsets of an image-finite poset X. We also show that A is isomorphic to its profinite completion iff A is finitely approximable, complete, and the kernel of every finite homomorphic image of A is a principal filter of A.      

Varieties of two-dimensional cylindric algebras.¶Part I: Diagonal-free case

We investigate the lattice of all subvarieties of the variety Df ₂ of two-dimensional diagonal-free cylindric algebras. We prove that a Df ₂-algebra is finitely representable if it is finitely approximable, characterize finite projective Df ₂-algebras, and show that there are no non-trivial injectives and absolute retracts in Df ₂. We prove that every proper subvariety of Df ₂ is locally finite, and hence Df ₂ is hereditarily finitely approximable. We describe all six critical varieties in , which leads to a characterization of finitely generated subvarieties of Df ₂. Finally, we describe all square representable and rectangularly representable subvarieties of Df ₂. Received May 25, 2000; accepted in final form November 2, 2001.     

On solvable groups,all proper factor groups of which have finite ranks

This paper deals with finitely generated finitely approximable solvable groups of infinite special rank, all proper normal subgroups of which determine the factor groups of finite special ranks.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 9, pp. 1274–1281, September, 1993.     

A Criterion for Admissibility of Inference Rules in Some Class of S4-Logics Without the Branching Property

We consider a finitely approximable modal S4-logic without the branching property. Although Rybakov's criterion is inapplicable, using his method we manage to obtain an algorithmic criterion for admissibility of inference rules in a given logic.     

Monotone thematic factorizations of matrix functions

We continue the study of the so-called thematic factorizations of admissible very badly approximable matrix functions. These factorizations were introduced by V.V. Peller and N.J. Young for studying superoptimal approximation by bounded analytic matrix functions. Even though thematic indices associated with a thematic factorization of an admissible very badly approximable matrix function are not uniquely determined by the function itself, R.B. Alexeev and V.V. Peller showed that the thematic indices of any monotone non-increasing thematic factorization of an admissible very badly approximable matrix function are uniquely determined. In this paper, we prove the existence of monotone non-decreasing thematic factorizations for admissible very badly approximable matrix functions. It is also shown that the thematic indices appearing in a monotone non-decreasing thematic factorization are not uniquely determined by the matrix function itself. Furthermore, we show that the monotone non-increasing thematic factorization gives rise to a great number of other thematic factorizations.     

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.     

Existence of sufficient regular conditional probabilities

If a-field is sufficient for a family of probability measures defined on a-field then there exist regular determinations of the conditional probability of P, given, which are independent of the special measure, provided that is-regular. A counterexample shows that the-regularity of cannot be replaced by the assumption that each is approximable by a fixed compact system. In particular if a-field is sufficient for a family of probability measures defined on a separable-field and if each admits a regular conditional probability, given, a common regular conditional probability, given, need not exist.     

Preservation of Admissibility of Inference Rules in the Logics Similar to S4.2

We show that an arbitrary finitely approximable logic extending S4.2(Grz.2,KC) preserves all admissible inference rules of the logic S4.2(Grz.2,KC) if and only if this logic possesses the so-called semantic cocovering property.     

Existence of self-similar energies on finitely ramified fractals

A self-similar energy on finitely ramified fractals can be constructed starting from an eigenform, i.e., an eigenvector of a special operator defined on the fractal. In this paper, we prove two existence results for regular eigenforms that consequently are existence results for self-similar energies on finitely ramified fractals. The first result proves the existence of a regular eigenform for suitable weights on fractals, assuming only that the boundary cells are separated and the union of the interior cells is connected. This result improves previous results and applies to many finitely ramified fractals usually considered. The second result proves the existence of a regular eigenform in the general case of finitely ramified fractals in a setting similar to that of P.C.F. self-similar sets considered, for example, by R. Strichartz in [11]. In this general case, however, the eigenform is not necessarily on the given structure, but is rather on only a suitable power of it. Nevertheless, as the fractal generated is the same as the original fractal, the result provides a regular self-similar energy on the given fractal.     

On krull overrings of a marot ring whose regular ideals are finitely generated ∗

Let R be a Marot ring whose regular ideals are finitely generated and D a Krull overring of R. In this paper, we show that if reg-dim R≥ 2, then each regular ideal of D is finitely generated and reg-dim D≥ 2. In particular, each regular ideal of a Krull overring of a Noetherijan ring R is finitely generated provided that (regular) Krull-dimension R≥ 2. This is a generalization of the well-known fact that a Krull overring of a Noetherian domain with Krull-dimension ≥ 2 is also a Noetherian domain with Krull-dimension ≥ 2.     

Continuous L-domains in logical form

We introduce a framework of approximable disjunctive propositional logic, which is the logic that results from a disjunctive propositional logic by adding an additional connective. The Lindenbaum algebra of this logic is an approximable dD-algebra. We show that for any approximable dD-algebra, its approximable filters ordered by set inclusion form a continuous L-domain. Conversely, every continuous L-domain can be represented as an approximable dD-algebra. Moreover, we establish a categorical equivalence between the category of approximable dD-algebras with approximable dD-algebra morphisms and that of continuous L-domains with Scott-continuous functions. This extends Abramsky's Domain Theory in Logical Form to the world of continuous L-domains. As an application, we give an affirmative answer to an open problem of Chen and Jung.     

正则WB-环

引进了WB-环,研究了正则环为WB-环的等价刻画．如果A是正则环R上的有限生成投射右模而且M_n(R)都是WB-环(n∈N),若B,C是任何右R-模而且A⊕B≌A⊕C,证明了存在正交理想I,J,使得B/BI■~⊕C/CI且C/CJ■~⊕B/BJ．这也给出了QB-环上新的模比较性质．     

On uniform permutations with finite dispersion parameters

We study the group G of uniform permutations of the set of integers with finite dispersion parameters. We prove that every finite subset of G lies in a subgroup of the form Q = AB, where A and B are locally finitely approximable subgroups of G.     

A result on the ideal structure of $$\mathcal L^r(X)$$ L r ( X ) for uniformly convex X

Positivity - We consider the question of when is every positive compact operator, between two given Banach lattices, approximable regular. An immediate consequence of our main result is that,...     

Equimorphy in varieties of distributive double p-algebras

Any finitely generated regular variety V of distributive double p-algebras is finitely determined, meaning that for some finite cardinal n(V), any subclass S V of algebras with isomorphic endomorphism monoids has fewer than n(V) pairwise non-isomorphic members. This result follows from our structural characterization of those finitely generated almost regular varieties which are finitely determined. We conjecture that any finitely generated, finitely determined variety of distributive double p-algebras must be almost regular.     

More on Comonotone Polynomial Approximation

The main achievement of this paper is that we show, what was to us, a surprising conclusion, namely, twice continuously differentiable functions in (0,1) (with some regular behavior at the endpoints) which change monotonicity at least once in the interval, are approximable better by comonotone polynomials, than are such functions that are merely monotone. We obtain Jackson-type estimates for the comonotone polynomial approximation of such functions that are impossible to achieve for monotone approximation. July 7, 1998. Date revised: May 5, 1999. Date accepted: July 23, 1999.     

On Regular Rings Satisfying Almost Comparability

In this article, we study regular rings satisfying almost comparability. We first show that, for regular rings, almost comparability is inherited by finitely generated projective modules and finite matrix rings, and, as a main result, we prove that the strict cancellation property holds for the family of all finitely generated projective modules over directly finite regular rings satisfying almost comparability.     

On the regular part of varieties of algebras

We show that the regular part of a variety of algebras may not consist entirely of subalgebras of Plonka sums; indeed, the latter may not be closed under homomorphic images. In addition we give an example of a finitely based variety whose regular part has no finite basis (but is finitely based in a different similarity type).Our examples contrast with known results for semigroups, and contradict a published claim for the general case.To the memory of András HuhnPresented by Boris Schein.