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  • Lattice-ordered pregroups are semi-distributive
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-20
    Nick Galatos, Peter Jipsen, Michael Kinyon, Adam Přenosil

    We prove that the lattice reduct of every lattice-ordered pregroup is semidistributive. This is a consequence of a certain weak form of the distributive law which holds in lattice-ordered pregroups.

    更新日期:2021-01-21
  • Sandwiches for promise constraint satisfaction
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-20
    Guofeng Deng, Ezzeddine El Sai, Trevor Manders, Peter Mayr, Poramate Nakkirt, Athena Sparks

    Promise Constraint Satisfaction Problems (\(\mathrm{PCSP}\)) were proposed recently by Brakensiek and Guruswami as a framework to study approximations for Constraint Satisfaction Problems (\(\mathrm{CSP}\)). Informally a \(\mathrm{PCSP}\) asks to distinguish between whether a given instance of a \(\mathrm{CSP}\) has a solution or not even a specified relaxation can be satisfied. All currently known

    更新日期:2021-01-21
  • Characterising certain compactifications of frames with special attention to Freudenthal
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-19
    Simo Mthethwa

    We introduce the definition of h-perfect elements relative to a compactification \(h:M\longrightarrow L\) and show that if a collection of all such elements is a basis, then the remainder of a frame in this compactification is zero-dimensional. This concept yields what we call a full \(\pi \)-compact basis for rim-compact frames. Compactifications arising from full \(\pi \)-compact bases are investigated

    更新日期:2021-01-19
  • Neutrabelian algebras
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-18
    Keith A. Kearnes, Connor Meredith, Ágnes Szendrei

    We introduce “neutrabelian algebras”, and prove that finite, hereditarily neutrabelian algebras with a cube term are dualizable.

    更新日期:2021-01-18
  • Solving a fixed number of equations over finite groups
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-14
    Philipp Nuspl

    We investigate the complexity of solving systems of polynomial equations over finite groups. In 1999 Goldmann and Russell showed \(\mathrm {NP}\)-completeness of this problem for non-Abelian groups. We show that the problem can become tractable for some non-Abelian groups if we fix the number of equations. Recently, Földvári and Horváth showed that a single equation over groups which are semidirect

    更新日期:2021-01-14
  • Existence of cube terms in finite algebras
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-12
    Alexandr Kazda, Dmitriy Zhuk

    We study the problem of whether a given finite algebra with finitely many basic operations contains a cube term; we give both structural and algorithmic results. We show that if such an algebra has a cube term then it has a cube term of dimension at most N, where the number N depends on the arities of basic operations of the algebra and the size of the basic set. For finite idempotent algebras we give

    更新日期:2021-01-13
  • Mal’cev conditions corresponding to identities for compatible reflexive relations
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-12
    Stefano Fioravanti

    We investigate Mal’cev conditions described by those equations whose variables runs over the set of all compatible reflexive relations. Let \(p \le q\) be an equation for the language \(\{\wedge , \circ ,+\}\). We give a characterization of the class of all varieties which satisfy \(p \le q\) over the set of all compatible reflexive relations. The aim is to find an analogon of the Pixley–Wille algorithm

    更新日期:2021-01-13
  • Sufficient conditions for the finiteness of the 3-generated lattice with modular and distributive type elements among generators
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-07
    Alexander G. Gein, Mikhail P. Shushpanov

    We investigate the finiteness and the infiniteness of the free 3-generated lattice with modular and distributive type elements among generators. For all triples of generators with modular and distributive type elements, it is discovered whether the lattice generated by such triple is finite or infinite.

    更新日期:2021-01-07
  • Invariance of projective modules in $$\mathsf {Sup}$$ Sup under self-duality
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-07
    Javier Gutiérrez García, Ulrich Höhle, Tomasz Kubiak

    Starting from enriched order-theoretic properties of modules over a unital quantale in the category \(\mathsf {Sup}\), this paper presents the following theorem. If the underlying quantale is unital and involutive with a designated element, then the duality of right (left) modules preserves projectivity if and only if the underlying quantale has a dualizing element.

    更新日期:2021-01-07
  • Epimorphisms in varieties of subidempotent residuated structures
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-04
    T. Moraschini, J. G. Raftery, J. J. Wannenburg

    A commutative residuated lattice \({\varvec{A}}\) is said to be subidempotent if the lower bounds of its neutral element e are idempotent (in which case they naturally constitute a Brouwerian algebra \({\varvec{A}}^-\)). It is proved here that epimorphisms are surjective in a variety \({\mathsf {K}}\) of such algebras \({\varvec{A}}\) (with or without involution), provided that each finitely subdirectly

    更新日期:2021-01-05
  • Results in L-algebras
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-04
    Lavinia Corina Ciungu

    We study some classes of L-algebras and we give characterizations of commutative KL-algebras and CL-algebras. It is proved that any commutative KL-algebra is a BCK-algebra and any self-similar CL-algebra is commutative. The commutative ideals are defined and studied, and it is proved that a CL-algebra is commutative if and only if all its ideals are commutative. We also present the L-algebras arising

    更新日期:2021-01-05
  • Remarks about the Q-lattice of the variety of lattices
    Algebra Univers. (IF 0.404) Pub Date : 2021-01-04
    M. E. Adams, W. Dziobiak

    Let L denote the Q-lattice of the variety \({\mathcal {V}}\) of lattices, i.e. the lattice of quasivarieties that are contained in \({\mathcal {V}}\). Let F denote the free lattice in \({\mathcal {V}}\) with \(\omega \) free generators and let Q(F) denote the quasivariety of lattices generated by F. Let Fin denote the collection of finite lattices which belong to Q(F) and let Q(Fin) denote the quasivariety

    更新日期:2021-01-04
  • The Tschantz and the alvin higher conditions are equivalent in congruence distributive varieties
    Algebra Univers. (IF 0.404) Pub Date : 2020-12-23
    Paolo Lipparini

    We show that, under the assumption of congruence distributivity, a condition by S. Tschantz characterizing congruence modularity is equivalent to a variant of the classical Jónsson condition. Here equivalence is intended in a strong sense, to the effect that the corresponding sequences of terms have exactly the same length.

    更新日期:2020-12-23
  • On Jónsson’s problem for groupoids of relations with operation of binary cylindrification
    Algebra Univers. (IF 0.404) Pub Date : 2020-11-16
    Dmitry A. Bredikhin

    In this paper, it is proved that the quasi-variety generated by the class of partially ordered groupoids of relations with the operation of binary cylindrification forms a variety.

    更新日期:2020-11-16
  • Lattices from graph associahedra and subalgebras of the Malvenuto–Reutenauer algebra
    Algebra Univers. (IF 0.404) Pub Date : 2020-11-12
    Emily Barnard, Thomas McConville

    The Malvenuto–Reutenauer algebra is a well-studied combinatorial Hopf algebra with a basis indexed by permutations. This algebra contains a wide variety of interesting sub Hopf algebras, in particular the Hopf algebra of plane binary trees introduced by Loday and Ronco. We compare two general constructions of subalgebras of the Malvenuto–Reutenauer algebra, both of which include the Loday–Ronco algebra

    更新日期:2020-11-12
  • Split epimorphisms as a productive tool in Universal Algebra
    Algebra Univers. (IF 0.404) Pub Date : 2020-11-10
    Dominique Bourn

    By various examples, we show how, in Universal Algebra, the choice of a class of split epimorphisms \(\Sigma \), defined by specific equations or local operations in their fibres, can be used as a productive and flexible tool determining \(\Sigma \)-partial properties. We focus, here, our attention on \(\Sigma \)-partial congruence modular and \(\Sigma \)-partial congruence distributive formulae.

    更新日期:2020-11-12
  • On the convergence rate of the fraction of simple algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-31
    Florian Aichinger

    We provide an improved lower bound for the convergence rate of the fraction of simple algebras using combinatorial arguments.

    更新日期:2020-11-02
  • Equidecomposable magmas
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-30
    Carles Cardó

    A magma is called equidecomposable when the operation is injective, or, in other words, if \(x+y=x'+y'\) implies that \(x=x'\) and \(y=y'\). A magma is free iff it is equidecomposable and graded, hence the notion of equidecomposability is very related to the notion of freeness although it is not sufficient. We study main properties of such magmas. In particular, an alternative characterization of freeness

    更新日期:2020-11-02
  • Properties not retained by pointed enrichments of finite lattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-30
    Ainur O. Basheyeva, Manat Mustafa, Anvar M. Nurakunov

    The present work considers algebras and their enrichments. It is shown by two examples of finite lattices that the properties “to have (no) a finite basis of quasi-identities” and “to generate a standard topological quasivariety” are not preserved with respect to pointed enrichments of finite algebras.

    更新日期:2020-11-02
  • Affine completeness of the algebra of full binary trees
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-30
    André Arnold, Patrick Cégielski, Serge Grigorieff, Irène Guessarian

    A function on an algebra is congruence preserving if, for any congruence, it maps pairs of congruent elements onto pairs of congruent elements. We show that on the algebra of full binary trees whose leaves are labeled by letters of an alphabet containing at least three letters, a function is congruence preserving if and only if it is polynomial. This exhibits an example of a non commutative and non

    更新日期:2020-11-02
  • Congruence lattices of connected monounary algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-30
    Danica Jakubíková-Studenovská, Lucia Janičková

    The system of all congruences of an algebra (A, F) forms a lattice, denoted \({{\,\mathrm{Con}\,}}(A, F)\). Further, the system of all congruence lattices of all algebras with the base set A forms a lattice \(\mathcal {E}_A\). We deal with meet-irreducibility in \(\mathcal {E}_A\) for a given finite set A. All meet-irreducible elements of \(\mathcal {E}_A\) are congruence lattices of monounary algebras

    更新日期:2020-10-30
  • Lattice Burnside rings
    Algebra Univers. (IF 0.404) Pub Date : 2020-10-21
    Fumihito Oda, Yugen Takegahara, Tomoyuki Yoshida

    Given a finite group G and a finite G-lattice \({{\mathscr {L}}}\), we introduce the concept of lattice Burnside ring associated to a family of nonempty sublattices \({{\mathscr {L}}}_H\) of \({{\mathscr {L}}}\) for \(H\le G\). The slice Burnside ring introduced by Bouc is isomorphic to a lattice Burnside ring. Any lattice Burnside ring is an extension of the ordinary Burnside ring and is isomorphic

    更新日期:2020-10-30
  • Closed sets of finitary functions between finite fields of coprime order
    Algebra Univers. (IF 0.404) Pub Date : 2020-09-27
    Stefano Fioravanti

    We investigate the finitary functions from a finite field \(\mathbb {F}_q\) to the finite field \(\mathbb {F}_p\), where p and q are powers of different primes. An \((\mathbb {F}_p,\mathbb {F}_q)\)-linearly closed clonoid is a subset of these functions which is closed under composition from the right and from the left with linear mappings. We give a characterization of these subsets of functions through

    更新日期:2020-09-28
  • Some structural and residual properties of 2-semilattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-09-13
    Ian Payne

    To each 2-semilattice, one can associate a digraph and a partial order. We analyze these two structures working toward two main goals: One goal is to give a structural dichotomy on minimal congruences of 2-semilattices. From this, we are able to deduce information about the tame-congruence-theoretic types that occur in 2-semilattices. In particular, we show that the type of a finite simple 2-semilattice

    更新日期:2020-09-13
  • Expanding Belnap: dualities for a new class of default bilattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-09-09
    Andrew P. K. Craig, Brian A. Davey, Miroslav Haviar
    更新日期:2020-09-10
  • Lattices do not distribute over powerset
    Algebra Univers. (IF 0.404) Pub Date : 2020-09-04
    Julián Salamanca Téllez

    We show that there is no distributive law of the free lattice monad over the powerset monad. The proof presented here also works for other classes of lattices such as (bounded) distributive/modular lattices and also for some variants of the powerset monad such as the (nonempty) finite powerset monad.

    更新日期:2020-09-05
  • On saturated varieties of posemigroups
    Algebra Univers. (IF 0.404) Pub Date : 2020-08-29
    Shabir Ahmad Ahanger, Aftab Hussain Shah, Noor Mohammad Khan

    We show that a permutative variety of posemigroups satisfying a permutation identity \(x_1x_2\cdots x_n=x_{i_1}x_{i_2}\cdots x_{i_n}\) with \(i_1\ne 1~ \text{ and }~i_{n-1}\ne n-1 ~[i_n\ne n~\text{ and }~i_{2}\ne 2]\) is saturated if and only if it admits an identity I such that I is not a permutation identity and at least one side of I has no repeated variables. Then we show that the variety of po-rectangular

    更新日期:2020-08-29
  • A note on the Knaster–Tarski Fixpoint Theorem
    Algebra Univers. (IF 0.404) Pub Date : 2020-08-09
    Mengqiao Huang, Yuxi Fu

    This note shows that several statements about fixpoints in order theory are equivalent to Knaster–Tarski Fixpoint Theorem for complete lattices. All proofs have been done in Zermelo–Fraenkel set theory without the Axiom of Choice.

    更新日期:2020-08-10
  • Representing subalgebras as retracts of finite subdirect powers
    Algebra Univers. (IF 0.404) Pub Date : 2020-08-06
    Keith A. Kearnes, Alexander Rasstrigin

    We prove that if \({\mathbb {A}}\) is an algebra that is supernilpotent with respect to the 2-term higher commutator, and \({\mathbb {B}}\) is a subalgebra of \({\mathbb {A}}\), then \({\mathbb {B}}\) is representable as a retract of a finite subdirect power of \(\mathbb A\).

    更新日期:2020-08-06
  • Lattice universality of locally finite 2-groups
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-20
    Vladimir B. Repnitskiǐ

    We prove that every algebraic lattice is isomorphic to a complete sublattice in the subgroup lattice of a suitable locally finite 2-group. In particular, every lattice is embeddable in the subgroup lattice of a locally finite 2-group.

    更新日期:2020-07-20
  • Test sets for equality of terms in the additive structure of ordinals augmented with right multiplication by $$\omega $$ ω
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-20
    Christian Choffrut, Serge Grigorieff

    We consider the additive structure of ordinals augmented with right multiplication by \(\omega \). We prove that two terms in the algebra are semantically equal if and only if they take the same value on all elements of a set containing 0 and at least one ordinal of each finite degree. Among these (so-called) test sets the most natural one is that obtained by considering 0 along with all \(\omega \)-powers

    更新日期:2020-07-20
  • Filter and weak link topologies
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-13
    Mohammad A. Ranjbar, Mahmood Pourgholamhossein

    In this paper we present the concept of weak link and weak link topology on lattice ordered groups and MV-algebras. We show that it is a locally solid group topology. In addition, we investigate the metrizability of a link topology.

    更新日期:2020-07-13
  • On geometric posets and partial matroids
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-13
    Branimir Šešelja, Anna Slivková, Andreja Tepavčević

    The aim of this paper is to extend the notions of geometric lattices, semimodularity and matroids in the framework of finite posets and related systems of sets. We define a geometric poset as one which is atomistic and which satisfies particular conditions connecting elements to atoms. Next, by using a suitable partial closure operator and the corresponding partial closure system, we define a partial

    更新日期:2020-07-13
  • Generalizing Galvin and Jónsson’s classification to $$N_5$$ N 5
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-13
    Brian T. Chan

    The problem of determining (up to lattice isomorphism) the lattices that are sublattices of free lattices is in general an extremely difficult and an unsolved problem. A notable result towards solving this problem was established by Galvin and Jónsson when they classified (up to lattice isomorphism) all of the distributive sublattices of free lattices in 1959. In this paper, we weaken the requirement

    更新日期:2020-07-13
  • Multiplayer rock–paper–scissors
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-08
    Charlotte Aten

    We study a class of algebras we regard as generalized rock–paper–scissors games. We determine when such algebras can exist, show that these algebras generate the varieties generated by hypertournament algebras, count these algebras, study their automorphisms, and determine their congruence lattices. We produce a family of finite simple algebras.

    更新日期:2020-07-08
  • The spectrum problem for Abelian $$\ell $$ ℓ -groups and MV-algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-07-06
    Giacomo Lenzi, Antonio Di Nola

    This paper deals with the problem of characterizing those topological spaces which are homeomorphic to the prime spectra of MV-algebras or Abelian \(\ell \)-groups. As a first main result, we show that a topological space X is the prime spectrum of an MV-algebra if and only if X is spectral, and the lattice K(X) of compact open subsets of X is a closed epimorphic image of the lattice of “cylinder rational

    更新日期:2020-07-06
  • The category of G-posets
    Algebra Univers. (IF 0.404) Pub Date : 2020-06-30
    Frank Murphy-Hernandez

    For a group G and a poset X, we say that X is a G-poset if it is equipped with a G-action that is monotone. If we consider the mononote G-equivariant maps as morphisms, then we get the category of G-posets. We give a description of the projective objects, injective objects, quotients, and generators.

    更新日期:2020-06-30
  • Essential adjunction of a strong unit to an archimedean lattice-ordered group
    Algebra Univers. (IF 0.404) Pub Date : 2020-06-22
    Anthony W. Hager, Philip Scowcroft

    Within archimedean \(\ell \)-groups, “\(H \in W^{*}\)” means H contains a strong unit, and “\(G \in SW^{*}\) (respectively, \(ESW^{*}\))” means there are \(H \in W^{*}\) and an embedding (respectively, essential embedding) \(G \le H\). This paper continues earlier work in which we developed methods of attacking the question “\(G \in SW^{*}\)?” and gave many examples with answer “No” and “Yes”. Here

    更新日期:2020-06-23
  • On semiconic idempotent commutative residuated lattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-06-19
    Wei Chen

    In this paper, we study semiconic idempotent commutative residuated lattices. An algebra of this kind is a semiconic generalized Sugihara monoid if it is generated by the lower bounds of the monoid identity. We establish a category equivalence between semiconic generalized Sugihara monoids and Brouwerian algebras with a strong nucleus. As an application, we show that central semiconic generalized Sugihara

    更新日期:2020-06-23
  • The structure of generalized BI-algebras and weakening relation algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-06-16
    Nikolaos Galatos, Peter Jipsen

    Generalized bunched implication algebras (GBI-algebras) are defined as residuated lattices with a Heyting implication, and are positioned between Boolean algebras with operators and lattices with operators. We characterize congruences on GBI-algebras by filters that are closed under Gumm–Ursini terms, and for involutive GBI-algebras these terms simplify to a dual version of the congruence term for

    更新日期:2020-06-16
  • Lifting, n -dimensional spectral resolutions, and n -dimensional observables
    Algebra Univers. (IF 0.404) Pub Date : 2020-06-07
    Anatolij Dvurečenskij, Dominik Lachman

    We show that under some natural conditions, we are able to lift an n-dimensional spectral resolution from one monotone \(\sigma \)-complete unital po-group into another one, when the first one is a \(\sigma \)-homomorphic image of the second one. We note that an n-dimensional spectral resolution is a mapping from \(\mathbb R^n\) into a quantum structure which is monotone, left-continuous with non-negative

    更新日期:2020-06-07
  • Semilattice sums of algebras and Mal’tsev products of varieties
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-20
    C. Bergman, T. Penza, A. B. Romanowska

    The Mal’tsev product of two varieties of similar algebras is always a quasivariety. We consider the question of when this quasivariety is a variety. The main result asserts that if \(\mathcal {V}\) is a strongly irregular variety with no nullary operations and at least one non-unary operation, and \(\mathcal {S}\) is the variety, of the same type as \(\mathcal {V}\), equivalent to the variety of semilattices

    更新日期:2020-05-20
  • Perfect locales and localic real functions
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-17
    Javier Gutiérrez García, Tomasz Kubiak, Jorge Picado

    The purpose of this paper is to identify the role of perfectness in the Michael insertion theorem for perfectly normal locales. We attain it by characterizing perfect locales in terms of strict insertion of two comparable lower semicontinuous and upper semicontinuous localic real functions. That characterization, when combined with the insertion theorem for normal locales, provides an improved formulation

    更新日期:2020-05-17
  • A non-finitely based involution semigroup of order five
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-14
    Meng Gao, Wen Ting Zhang, Yan Feng Luo

    Since the 1970s, the smallest known non-finitely based involution semigroups are of order six. This paper exhibits the first example of a non-finitely based involution semigroup of order five.

    更新日期:2020-05-14
  • Rings in which idempotents generate maximal or minimal ideals
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-08
    Themba Dube, Mojtaba Ghirati, Sajad Nazari, Ali Taherifar

    We characterize rings in which every left ideal generated by an idempotent different from 0 and 1 is either a maximal left ideal or a minimal left ideal. In the commutative case, we give a characterization in terms of topological properties of the maximal spectrum with the Zariski topology. We also consider a strictly weaker variant of this property, defined almost similarly, and characterize those

    更新日期:2020-05-08
  • On epimorphisms of ordered algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-05
    Nasir Sohail, Boža Tasić

    We prove that epimorphisms are surjective in certain categories of ordered \(\mathcal {F}\)-algebras. It then turns out that epimorphisms are also surjective in the category of all (unordered) algebras of type \(\mathcal {F}\).

    更新日期:2020-05-05
  • Structure theorems for idempotent residuated lattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-05-04
    José Gil-Férez, Peter Jipsen, George Metcalfe

    In this paper we study structural properties of residuated lattices that are idempotent as monoids. We provide descriptions of the totally ordered members of this class and obtain counting theorems for the number of finite algebras in various subclasses. We also establish the finite embeddability property for certain varieties generated by classes of residuated lattices that are conservative in the

    更新日期:2020-05-04
  • The structure group of a non-degenerate effect algebra
    Algebra Univers. (IF 0.404) Pub Date : 2020-04-27
    Carsten Dietzel, Wolfgang Rump

    A (non-commutative) structure group G(E) is associated to an arbitrary effect algebra E, and a concept of non-degeneracy is introduced. If E is non-degenerate, G(E) has a right invariant partial order, E embeds as an interval into G(E), and the negative cone of G(E) is a self-similar partial L-algebra. In the degenerate case, the possible anomalies are explained. Lattice effect algebras, 2-divisible

    更新日期:2020-04-27
  • Identical inclusions of semilattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-04-21
    G. Mashevitzky

    The class of identical inclusions was defined by Lyapin. We prove that any set of identical inclusions in the class of semilattices is equivalent to an elementary (the first order) formula. Elementary identical inclusions forms the class of universal formulas which is situated strictly between identities and universal positive formulas. We describe the infinite lattice of all classes of semilattices

    更新日期:2020-04-21
  • Finitary shadows of compact subgroups of $$S(\omega )$$S(ω)
    Algebra Univers. (IF 0.404) Pub Date : 2020-04-11
    B. Majcher-Iwanow

    Let LF be the lattice of all subgroups of the group \(SF(\omega )\) of all finitary permutations of the set of natural numbers. We consider subgroups of \(SF(\omega )\) of the form \(C\cap SF(\omega )\), where C is a compact subgroup of the group of all permutations. In particular, we study their distribution among elements of LF. We measure this using natural relations of orthogonality and almost

    更新日期:2020-04-11
  • Lattices and quantales of ideals of semigroups and their preservation under Morita contexts
    Algebra Univers. (IF 0.404) Pub Date : 2020-04-10
    Valdis Laan, László Márki, Ülo Reimaa

    We study properties of the lattice of unitary ideals of a semigroup. In particular, we show that it is a quantale. We prove that if two semigroups are connected by an acceptable Morita context then there is an isomorphism between the quantales of unitary ideals of these semigroups. Moreover, factorisable ideals corresponding to each other under this isomorphism are strongly Morita equivalent.

    更新日期:2020-04-10
  • Free and cofree S -quantales
    Algebra Univers. (IF 0.404) Pub Date : 2020-04-02
    Xin Zhang, Bin Zhao

    In this paper, we give an alternative representation of a free S-quantale over a poset. Furthermore, we give the concrete forms of free and cofree S-quantales over a sup-lattice. Finally, we give an example to present that a cofree S-quantale over a poset does not always exist.

    更新日期:2020-04-02
  • Two-element structures modulo primitive positive constructability
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-31
    Manuel Bodirsky, Albert Vucaj

    Primitive positive constructions have been introduced in recent work of Barto, Opršal, and Pinsker to study the computational complexity of constraint satisfaction problems. Let \({\mathfrak {P}}_{\mathrm {fin}}\) be the poset which arises from ordering all finite relational structures by pp-constructability. This poset is infinite, but we do not know whether it is uncountable. In this article, we

    更新日期:2020-03-31
  • On the structure of C -algebras through atomicity and if-then-else
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-31
    Gayatri Panicker, K. V. Krishna, Purandar Bhaduri

    This paper investigates the notions of atoms and atomicity in C-algebras and obtains a characterisation of atoms in the C-algebra of transformations. In this connection, various characterisations for the existence of suprema of subsets of C-algebras are obtained. Further, this work presents some necessary conditions and some sufficient conditions for the atomicity of C-algebras and shows that the class

    更新日期:2020-03-31
  • Varieties of semiassociative relation algebras and tense algebras
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-31
    James M. Koussas, Tomasz Kowalski

    It is well known that the subvariety lattice of the variety of relation algebras has exactly three atoms. The (join-irreducible) covers of two of these atoms are known, but a complete classification of the (join-irreducible) covers of the remaining atom has not yet been found. These statements are also true of a related subvariety lattice, namely the subvariety lattice of the variety of semiassociative

    更新日期:2020-03-31
  • On difunctionality of class relations
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-30
    Michael Hoefnagel, Zurab Janelidze, Diana Rodelo

    For a given variety \({\mathcal {V}}\) of algebras, we define a class relation to be a binary relation \(R\subseteq S^2\) which is of the form \(R=S^2\cap K\) for some congruence class K on \(A^2\), where A is an algebra in \( {\mathcal {V}}\) such that \(S\subseteq A\). In this paper we study the following property of \({\mathcal {V}}\): every reflexive class relation is an equivalence relation. In

    更新日期:2020-03-30
  • Connected monads weakly preserve products
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-30
    H. Peter Gumm

    If F is a (not necessarily associative) monad on Set, then the natural transformation \(F(A\times B)\rightarrow F(A)\times F(B)\) is surjective if and only if \(F(\varvec{1})=\varvec{1}\). Specializing F to \(F_{\mathcal {V}}\), the free algebra functor for a variety \(\mathcal {V},\) this result generalizes and clarifies an observation by Dent, Kearnes and Szendrei in 2012.

    更新日期:2020-03-30
  • Locales whose coz-complemented cozero sublocales have open closures
    Algebra Univers. (IF 0.404) Pub Date : 2020-03-29
    Oghenetega Ighedo, Martin M. Mugochi

    A cozero sublocale C of a completely regular locale L will here be called coz-complemented if there is a cozero sublocale D of L such that \(C\cap D\) is the void sublocale and \(C\vee D\) is dense in L. Following terminology in spaces, we say L is a cloz-locale if every coz-complemented sublocale of L has an open closure. We characterize cloz-locales in terms of certain embeddings, and also in terms

    更新日期:2020-03-29
  • Joins and Maltsev products of congruence permutable varieties
    Algebra Univers. (IF 0.404) Pub Date : 2020-02-25
    Clifford Bergman

    Let \(\mathcal {A}\) and \(\mathcal {B}\) be idempotent varieties and suppose that the variety \(\mathcal {A} \vee \mathcal {B} \) is congruence permutable. Then the Maltsev product \(\mathcal {A} \circ \mathcal {B} \) is also congruence permutable.

    更新日期:2020-02-25
  • Notes on planar semimodular lattices. VIII. Congruence lattices of SPS lattices
    Algebra Univers. (IF 0.404) Pub Date : 2020-02-22
    G. Grätzer

    In this note, I find a new property of the congruence lattice, \({{\,\mathrm{Con}\,}}L\), of an SPS lattice L (slim, planar, semimodular, where “slim” is the absence of \({\mathsf {M}}_3\) sublattices) with more than 2 elements: there are at least two dual atoms in\({{\,\mathrm{Con}\,}}L\). So the three-element chain cannot be represented as the congruence lattice of an SPS lattice, supplementing a result

    更新日期:2020-02-22
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