Semigroup ForumPub Date : 2024-05-28DOI: 10.1007/s00233-024-10438-6
G. Mashevitzky
{"title":"Small and countable inclusive varieties of semigroups","authors":"G. Mashevitzky","doi":"10.1007/s00233-024-10438-6","DOIUrl":"https://doi.org/10.1007/s00233-024-10438-6","url":null,"abstract":"<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.These universal formulas can be written as identical equalities of subsets of <span>(X^+)</span>. Classes of semigroups defined by identical inclusions are called inclusive varieties. We describe finite inclusive varieties of semigroups and study countable inclusive varieties of semigroups.We also describe small inclusive varieties, that is, inclusive varieties with finite lattices of their inclusive subvarieties, of completely regular semigroups and study inclusive varieties of completely regular semigroups with countable lattices of their inclusive subvarieties</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"9 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141169439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-05-23DOI: 10.1007/s00233-024-10434-w
Carlos A. M. André, Inês Legatheaux Martins
{"title":"Schur–Weyl dualities for the rook monoid: an approach via Schur algebras","authors":"Carlos A. M. André, Inês Legatheaux Martins","doi":"10.1007/s00233-024-10434-w","DOIUrl":"https://doi.org/10.1007/s00233-024-10434-w","url":null,"abstract":"<p>The rook monoid, also known as the symmetric inverse monoid, is the archetypal structure when it comes to extend the principle of symmetry. In this paper, we establish a Schur–Weyl duality between this monoid and an extension of the classical Schur algebra, which we name the extended Schur algebra. We also explain how this relates to Solomon’s Schur–Weyl duality between the rook monoid and the general linear group and mention some advantages of our approach.</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"37 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141149347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-05-03DOI: 10.1007/s00233-024-10431-z
T. D. H. Coleman, J. D. Mitchell, F. L. Smith, M. Tsalakou
{"title":"The Todd–Coxeter algorithm for semigroups and monoids","authors":"T. D. H. Coleman, J. D. Mitchell, F. L. Smith, M. Tsalakou","doi":"10.1007/s00233-024-10431-z","DOIUrl":"https://doi.org/10.1007/s00233-024-10431-z","url":null,"abstract":"<p>In this paper we provide an account of the Todd–Coxeter algorithm for computing congruences on semigroups and monoids. We also give a novel description of an analogue for semigroups of the so-called Felsch strategy from the Todd–Coxeter algorithm for groups.\u0000</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"14 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140883854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-22DOI: 10.1007/s00233-024-10430-0
Peter M. Higgins
{"title":"Finite regular semigroups with permutations that map elements to inverses","authors":"Peter M. Higgins","doi":"10.1007/s00233-024-10430-0","DOIUrl":"https://doi.org/10.1007/s00233-024-10430-0","url":null,"abstract":"<p>We give an account on what is known on the subject of <i>permutation matchings</i>, which are bijections of a finite regular semigroup that map each element to one of its inverses. This includes partial solutions to some open questions, including a related novel combinatorial problem.</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"101 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140800084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-17DOI: 10.1007/s00233-024-10427-9
Dmitry Kudryavtsev
{"title":"Restrictions on local embeddability into finite semigroups","authors":"Dmitry Kudryavtsev","doi":"10.1007/s00233-024-10427-9","DOIUrl":"https://doi.org/10.1007/s00233-024-10427-9","url":null,"abstract":"<p>We expand the concept of local embeddability into finite structures (LEF) for the class of semigroups with investigations of non-LEF structures, a closely related generalising property of local wrapping of finite structures (LWF) and inverse semigroups. The established results include a description of a family of non-LEF semigroups unifying the bicyclic monoid and Baumslag–Solitar groups and demonstrating that inverse LWF semigroups with finite number of idempotents are LEF.</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"49 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615840","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-16DOI: 10.1007/s00233-024-10429-7
P. A. García-Sánchez
{"title":"The isomorphism problem for ideal class monoids of numerical semigroups","authors":"P. A. García-Sánchez","doi":"10.1007/s00233-024-10429-7","DOIUrl":"https://doi.org/10.1007/s00233-024-10429-7","url":null,"abstract":"<p>From any poset isomorphic to the poset of gaps of a numerical semigroup <i>S</i> with the order induced by <i>S</i>, one can recover <i>S</i>. As an application, we prove that two different numerical semigroups cannot have isomorphic posets (with respect to set inclusion) of ideals whose minimum is zero. We also show that given two numerical semigroups <i>S</i> and <i>T</i>, if their ideal class monoids are isomorphic, then <i>S</i> must be equal to <i>T</i>.\u0000</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"1 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-16DOI: 10.1007/s00233-024-10428-8
Simon M. Goberstein
{"title":"Lattice isomorphisms of orthodox semigroups with no nontrivial finite subgroups","authors":"Simon M. Goberstein","doi":"10.1007/s00233-024-10428-8","DOIUrl":"https://doi.org/10.1007/s00233-024-10428-8","url":null,"abstract":"<p>Two semigroups are lattice isomorphic if their subsemigroup lattices are isomorphic, and a class of semigroups is lattice closed if it contains every semigroup which is lattice isomorphic to some semigroup from that class. An orthodox semigroup is a regular semigroup whose idempotents form a subsemigroup. We prove that the class of all orthodox semigroups having no nontrivial finite subgroups is lattice closed.</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"20 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-16DOI: 10.1007/s00233-024-10425-x
Ali Barzanouni, Somayyeh Jangjooye Shaldehi
{"title":"Topological sensitivity for semiflow","authors":"Ali Barzanouni, Somayyeh Jangjooye Shaldehi","doi":"10.1007/s00233-024-10425-x","DOIUrl":"https://doi.org/10.1007/s00233-024-10425-x","url":null,"abstract":"<p>We give a pointwise version of sensitivity in terms of open covers for a semiflow (<i>T</i>, <i>X</i>) of a topological semigroup <i>T</i> on a Hausdorff space <i>X</i> and call it a Hausdorff sensitive point. If <span>((X, {mathscr {U}}))</span> is a uniform space with topology <span>(tau )</span>, then the definition of Hausdorff sensitivity for <span>((T, (X, tau )))</span> gives a pointwise version of sensitivity in terms of uniformity and we call it a uniformly sensitive point. For a semiflow (<i>T</i>, <i>X</i>) on a compact Hausdorff space <i>X</i>, these notions (i.e. Hausdorff sensitive point and uniformly sensitive point) are equal and they are <i>T</i>-invariant if <i>T</i> is a <i>C</i>-semigroup. They are not preserved by factor maps and subsystems, but behave slightly better with respect to lifting. We give the definition of a topologically equicontinuous pair for a semiflow (<i>T</i>, <i>X</i>) on a topological space <i>X</i> and show that if (<i>T</i>, <i>X</i>) is a topologically equicontinuous pair in (<i>x</i>, <i>y</i>), for all <span>(yin X)</span>, then <span>(overline{Tx}= D_T(x))</span> where </p><span>$$begin{aligned} D_T(x)= bigcap { overline{TU}: text { for all open neighborhoods}, U, text {of}, x }. end{aligned}$$</span><p>We prove for a topologically transitive semiflow (<i>T</i>, <i>X</i>) of a <i>C</i>-semigroup <i>T</i> on a regular space <i>X</i> with a topologically equicontinuous point that the set of topologically equicontinuous points coincides with the set of transitive points. This implies that every minimal semiflow of <i>C</i>-semigroup <i>T</i> on a regular space <i>X</i> with a topologically equicontinuous point is topologically equicontinuous. Moreover, we show that if <i>X</i> is a regular space and (<i>T</i>, <i>X</i>) is not a topologically equicontinuous pair in (<i>x</i>, <i>y</i>), then <i>x</i> is a Hausdorff sensitive point for (<i>T</i>, <i>X</i>). Hence, a minimal semiflow of a <i>C</i>-semigroup <i>T</i> on a regular space <i>X</i> is either topologically equicontinuous or topologically sensitive.\u0000</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"99 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-12DOI: 10.1007/s00233-024-10426-w
Nils Olsson, Christopher O’Neill, Derek Rawling
{"title":"Atomic density of arithmetical congruence monoids","authors":"Nils Olsson, Christopher O’Neill, Derek Rawling","doi":"10.1007/s00233-024-10426-w","DOIUrl":"https://doi.org/10.1007/s00233-024-10426-w","url":null,"abstract":"<p>Consider the set <span>(M_{a,b} = {n in mathbb {Z}_{ge 1}: n equiv a bmod b} cup {1})</span> for <span>(a, b in mathbb {Z}_{ge 1})</span>. If <span>(a^2 equiv a bmod b)</span>, then <span>(M_{a,b})</span> is closed under multiplication and known as an arithmetic congruence monoid (ACM). A non-unit <span>(n in M_{a,b})</span> is an atom if it cannot be expressed as a product of non-units, and the atomic density of <span>(M_{a,b})</span> is the limiting proportion of elements that are atoms. In this paper, we characterize the atomic density of <span>(M_{a,b})</span> in terms of <i>a</i> and <i>b</i>.\u0000</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"73 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140577889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Semigroup ForumPub Date : 2024-04-09DOI: 10.1007/s00233-024-10423-z
Bhavya Agrawalla, Nasief Khlaif, Haynes Miller
{"title":"The André–Quillen cohomology of commutative monoids","authors":"Bhavya Agrawalla, Nasief Khlaif, Haynes Miller","doi":"10.1007/s00233-024-10423-z","DOIUrl":"https://doi.org/10.1007/s00233-024-10423-z","url":null,"abstract":"<p>We observe that Beck modules for a commutative monoid are exactly modules over a graded commutative ring associated to the monoid. Under this identification, the Quillen cohomology of commutative monoids is a special case of the André–Quillen cohomology for graded commutative rings, generalizing a result of Kurdiani and Pirashvili. To verify this we develop the necessary grading formalism. The partial cochain complex developed by Pierre Grillet for computing Quillen cohomology appears as the start of a modification of the Harrison cochain complex suggested by Michael Barr.</p>","PeriodicalId":49549,"journal":{"name":"Semigroup Forum","volume":"35 1","pages":""},"PeriodicalIF":0.7,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140577793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}