{"title":"Some generalized metric properties of n-semitopological groups","authors":"Fucai Lin, Xixi Qi","doi":"10.1007/s00012-025-00897-5","DOIUrl":"10.1007/s00012-025-00897-5","url":null,"abstract":"<div><p>A semitopological group <i>G</i> is said to be an <i>n-semitopological group</i>, if for any <span>(gin G)</span> with <span>(enot in overline{{g}})</span> there is a neighborhood <i>W</i> of <i>e</i> such that <span>(gnot in W^{n})</span>, where <span>(nin mathbb {N})</span>. The class of <i>n</i>-semitopological groups (<span>(nge 2)</span>) contains the class of paratopological groups and Hausdorff quasi-topological groups. Fix any <span>(nin mathbb {N})</span>. Properties of <i>n</i>-semitopological groups are studied, and questions about <i>n</i>-semitopological groups are posed. Some generalized metric properties of <i>n</i>-semitopological groups are discussed, which contains mainly results are that (1) each Hausdorff first-countable 2-semitopological group admits a coarser semi-metrizable topology; (2) each locally compact, Baire and <span>(sigma )</span>-compact 2-semitopological group is a topological group; (3) the condensation of some kind of 2-semitopological groups topologies are given. Finally, some cardinal invariants of <i>n</i>-semitopological groups are discussed.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"u-topology and m-topology on the ring of measurable functions, generalized and revisited","authors":"Sudip Kumar Acharyya, Atasi Debray, Pratip Nandi","doi":"10.1007/s00012-025-00896-6","DOIUrl":"10.1007/s00012-025-00896-6","url":null,"abstract":"<div><p>Given an ideal <i>I</i> in the ring <span>(mathcal {M}(X,mathcal {A}))</span> of all real valued measurable functions over the measurable space <span>((X,mathcal {A}))</span> and a measure <span>(mu :mathcal {A}rightarrow [0,infty ])</span>, we introduce the <span>(u_mu ^I)</span>-topology and the <span>(m_mu ^I)</span>-topology on <span>(mathcal {M}(X,mathcal {A}))</span> as generalizations of the <i>u</i>-topology and the <i>m</i>-topology on <span>(mathcal {M}(X,mathcal {A}))</span> respectively. For a countably generated ideal <i>I</i> in <span>(mathcal {M}(X,mathcal {A}))</span>, it is proved that the <span>(u_mu ^I)</span>-topology and the <span>(m_mu ^I)</span>-topology coincide if and only if <span>(Xsetminus bigcap Z[I])</span> is a <span>(mu )</span>-bounded subset of <i>X</i>. The components of 0 in both of these topologies are determined and it is proved that the condition of denseness of an ideal <i>I</i> in <span>(mathcal {M}(X,mathcal {A}))</span> is equivalent in these two topologies and this happens when and only when there exists <span>(Zin Z[I])</span> such that <span>(mu (Z)=0)</span>. It is also proved that <i>I</i> is closed in <span>(mathcal {M}(X,mathcal {A}))</span> in the <span>(m_mu )</span>-topology if and only if it is a <span>(Z_mu )</span>-ideal. Two more topologies on <span>(mathcal {M}(X,mathcal {A}))</span> viz. the <span>(u_{mu ,F}^I)</span>-topology and the <span>(m_{mu ,F}^I)</span>-topology, finer than the <span>(u_mu ^I)</span>-topology and the <span>(m_mu ^I)</span>-topology respectively are introduced and a few relevant properties are investigated thereon.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Infinitary primitive positive definability over the real numbers with convex relations","authors":"Sebastian Meyer","doi":"10.1007/s00012-025-00893-9","DOIUrl":"10.1007/s00012-025-00893-9","url":null,"abstract":"<div><p>On a finite structure, the polymorphism invariant relations are exactly the primitively positively definable relations. On infinite structures, these two sets of relations are different in general. Infinitarily primitively positively definable relations are a natural intermediate concept which extends primitive positive definability by infinite conjunctions. We consider for every convex set <span>(Ssubseteq {mathbb {R}}^n)</span> the structure of the real numbers <span>({mathbb {R}})</span> with addition, scalar multiplication, constants, and additionally the relation <i>S</i>. We prove that depending on <i>S</i>, the set of all relations with an infinitary primitive positive definition in this structure equals one out of six possible sets. This dependency gives a natural partition of the convex sets into six nonempty classes. We also give an elementary geometric description of the classes and a description in terms of linear maps. The classification also implies that there is no locally closed clone between the clone of affine combinations and the clone of convex combinations.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00012-025-00893-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Perspectivity in complemented modular lattices and regular rings","authors":"Christian Herrmann","doi":"10.1007/s00012-025-00894-8","DOIUrl":"10.1007/s00012-025-00894-8","url":null,"abstract":"<div><p>Based on an analogue for systems of partial isomorphisms between lower sections in a complemented modular lattice we construct a series of terms (including inner inverse as basic operation and providing descending chains) such that principal right ideals <span>(aR cong bR)</span> in a (von Neumann) regular ring <i>R</i> are perspective if the series becomes stationary. In particular, this applies if <span>(aR cap bR)</span> is of finite height in <i>L</i>(<i>R</i>). This is used to derive, for existence-varieties <span>(mathcal {V})</span> of regular rings, equivalence of unit-regularity and direct finiteness, both conceived as a property shared by all members of <span>(mathcal {V})</span>.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the completeness of localic groups via generators and relations","authors":"Simo S. Mthethwa, Onesipho Ntombela","doi":"10.1007/s00012-025-00898-4","DOIUrl":"10.1007/s00012-025-00898-4","url":null,"abstract":"<div><p>In the late ‘90s, Banaschewski and Vermeulen showed that any localic group is complete in its two-sided uniformity. In this paper, we provide a method of constructing extensions of localic groups. The raison d’être of this paper, however, is to show using generators and relations that if the left and the right uniformity coincide, then the localic group must be complete.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00012-025-00898-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145144176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Miguel Campercholi, Diego Castaño, Gonzalo Zigarán
{"title":"Congruence systems in dual discriminator varieties","authors":"Miguel Campercholi, Diego Castaño, Gonzalo Zigarán","doi":"10.1007/s00012-025-00891-x","DOIUrl":"10.1007/s00012-025-00891-x","url":null,"abstract":"<div><p>A <i>congruence system</i> on an algebra <span>(textbf{A})</span> is a tuple <span>(langle theta _1,ldots ,theta _k,)</span> <span>(a_1,ldots ,a_krangle )</span> where <span>(theta _1,ldots ,theta _k in mathop {textrm{Con}}textbf{A})</span>, <span>(a_1,ldots ,a_k in A)</span> and <span>(langle a_i,a_jrangle in theta _i vee theta _j)</span> for all <span>(i,j in {1,ldots ,k})</span>. A <i>solution</i> to such a congruence system is an element <span>(a in A)</span> satisfying <span>(langle a,a_irangle in theta _i)</span> for all <span>(i in {1,ldots ,k})</span>. A tuple of congruences <span>(langle theta _1,ldots , theta _krangle )</span> is said to be a <i>Chinese Remainder tuple</i> (CR tuple for short) of <span>(textbf{A})</span> provided that every system <span>(langle theta _1,ldots ,theta _k,a_1,ldots ,a_krangle )</span> with <span>(a_1,ldots ,a_k in A)</span> has a solution. Since two congruences <span>(theta _1,theta _2)</span> form a CR tuple if and only if they permute, the property of being a CR tuple is a generalization of the notion of permutability that makes sense for more than two congruences. The main result of this article is a characterization of CR tuples for finite algebras in dual discriminator varieties. As an application, we obtain a neat characterization of CR tuples for finite distributive lattices.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145145547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Profinite bi-Heyting algebras","authors":"Lydia Tasiou","doi":"10.1007/s00012-025-00892-w","DOIUrl":"10.1007/s00012-025-00892-w","url":null,"abstract":"<div><p>A poset <span>({mathbb {X}})</span> is said to be zigzag image-finite, if the least updownset (i.e., both an upset and a downset) containing <i>x</i> is finite, for all <span>(xin X.)</span> We show that a bi-Heyting algebra is profinite if and only if it is isomorphic to the lattice of upsets of a zigzag image-finite poset. Zigzag image-finite posets have the property of being disjoint unions of finite connected posets. Because of this, we equivalently show that a bi-Heyting algebra is profinite if and only if it is isomorphic to a direct product of simple finite bi-Heyting algebras.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 3","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00012-025-00892-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143930124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali Akbar Estaji, Rahimeh Pourkhandani, Mehdi Vatandoost
{"title":"Compact ICA-topobooleans and the Smirnov compactification theorem","authors":"Ali Akbar Estaji, Rahimeh Pourkhandani, Mehdi Vatandoost","doi":"10.1007/s00012-025-00885-9","DOIUrl":"10.1007/s00012-025-00885-9","url":null,"abstract":"<div><p>Recently, the concepts of topoframe and topoboolean have been introduced as a generalization of point-free topology, and the relation between topobooleans and complete I-contact algebras (ICAs) has been studied. In this paper, we first introduce the ICA-topoboolean <span>(B_{tau (C)})</span>, in which <span>(tau (C))</span> is induced from the complete ICA (<i>B</i>, <i>C</i>), and then characterize compact atomic ICA-topobooleans by their point clusters. As an example of the noncompact case, we determine all clusters of <span>(big ( mathcal {P}(mathbb {R}), Cbig ))</span>, an ICA on the Boolean algebra of the power set of real numbers <span>(mathbb {R})</span>. Finally, we generalize the Smirnov compactification theorem from proximity spaces to atomic ICA-topobooleans.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143793114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Nonelementary inclusive varieties of groups and semigroups","authors":"G. Mashevitzky","doi":"10.1007/s00012-025-00887-7","DOIUrl":"10.1007/s00012-025-00887-7","url":null,"abstract":"<div><p>The class of identical inclusions was defined by E. S. Lyapin. This is the class of universal formulas which is situated strictly between identities and universal positive formulas. Classes of semigroups defined by identical inclusions are called inclusive varieties. Inclusive varieties that cannot be defined by the first order formulas are called nonelementary inclusive varieties. We study nonelementary inclusive varieties of groups, Clifford semigroups and nilsemigroups. In particular, a criterion for an inclusive variety to be nonelementary is found and limit nonelementary inclusive varieties of abelian groups are described. We also describe the upper semilattice of nonelementary inclusive varieties of finite abelian groups and prove that it is uncountable. We find an uncountable set of nonelementary inclusive varieties of nilpotent class 3 and nil class 2 finite commutative semigroups and a limit nonelementary inclusive variety of nilsemigroups. We consider completely regular semigroups in semigroup signature with an additional unary operation and nilsemigroups in semigroup signature with the additional constant 0.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00012-025-00887-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143778067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On the structure of modal and tense operators on a boolean algebra","authors":"Guram Bezhanishvili, Andre Kornell","doi":"10.1007/s00012-025-00890-y","DOIUrl":"10.1007/s00012-025-00890-y","url":null,"abstract":"<div><p>We initiate the study of the poset <span>(mathcal{N}mathcal{O}(B))</span> of necessity operators on a boolean algebra <i>B</i>. We show that <span>(mathcal{N}mathcal{O}(B))</span> is a meet-semilattice that need not be distributive. However, when <i>B</i> is complete, <span>(mathcal{N}mathcal{O}(B))</span> is necessarily a frame, which is spatial iff <i>B</i> is atomic. In that case, <span>(mathcal{N}mathcal{O}(B))</span> is a locally Stone frame. Dual results hold for the poset <span>(mathcal{P}mathcal{O}(B))</span> of possibility operators. We also obtain similar results for the posets <span>(mathcal {TNO}(B))</span> and <span>(mathcal {TPO}(B))</span> of tense necessity and possibility operators on <i>B</i>. Our main tool is Jónsson-Tarski duality, by which such operators correspond to continuous and interior relations on the Stone space of <i>B</i>.</p></div>","PeriodicalId":50827,"journal":{"name":"Algebra Universalis","volume":"86 2","pages":""},"PeriodicalIF":0.6,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143778068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}