Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106033
Dimitri Leemans , Klara Stokes , Philippe Tranchida
Recently, Leemans and Stokes constructed an infinite family of incidence geometries admitting trialities but no dualities from the groups (where with p a prime and a positive integer). Unfortunately, these geometries are not flag transitive. In this paper, we work with the Suzuki groups , where with e a positive integer and is divisible by 3. For any odd integer m dividing , or (i.e.: m is the order of some non-involutive element of ), we construct geometries of type that admit trialities but no dualities. We then prove that they are flag transitive when , no matter the value of q. These geometries form the first infinite family of incidence geometries of rank 3 that are flag transitive and have trialities but no dualities. They are constructed using chamber systems and the trialities come from field automorphisms. These same geometries can also be considered as regular hypermaps with automorphism group .
{"title":"Flag transitive geometries with trialities and no dualities coming from Suzuki groups","authors":"Dimitri Leemans , Klara Stokes , Philippe Tranchida","doi":"10.1016/j.jcta.2025.106033","DOIUrl":"10.1016/j.jcta.2025.106033","url":null,"abstract":"<div><div>Recently, Leemans and Stokes constructed an infinite family of incidence geometries admitting trialities but no dualities from the groups <span><math><mi>P</mi><mi>S</mi><mi>L</mi><mo>(</mo><mn>2</mn><mo>,</mo><mi>q</mi><mo>)</mo></math></span> (where <span><math><mi>q</mi><mo>=</mo><msup><mrow><mi>p</mi></mrow><mrow><mn>3</mn><mi>n</mi></mrow></msup></math></span> with <em>p</em> a prime and <span><math><mi>n</mi><mo>></mo><mn>0</mn></math></span> a positive integer). Unfortunately, these geometries are not flag transitive. In this paper, we work with the Suzuki groups <span><math><mi>S</mi><mi>z</mi><mo>(</mo><mi>q</mi><mo>)</mo></math></span>, where <span><math><mi>q</mi><mo>=</mo><msup><mrow><mn>2</mn></mrow><mrow><mn>2</mn><mi>e</mi><mo>+</mo><mn>1</mn></mrow></msup></math></span> with <em>e</em> a positive integer and <span><math><mn>2</mn><mi>e</mi><mo>+</mo><mn>1</mn></math></span> is divisible by 3. For any odd integer <em>m</em> dividing <span><math><mi>q</mi><mo>−</mo><mn>1</mn></math></span>, <span><math><mi>q</mi><mo>+</mo><msqrt><mrow><mn>2</mn><mi>q</mi></mrow></msqrt><mo>+</mo><mn>1</mn></math></span> or <span><math><mi>q</mi><mo>−</mo><msqrt><mrow><mn>2</mn><mi>q</mi></mrow></msqrt><mo>+</mo><mn>1</mn></math></span> (i.e.: <em>m</em> is the order of some non-involutive element of <span><math><mi>S</mi><mi>z</mi><mo>(</mo><mi>q</mi><mo>)</mo></math></span>), we construct geometries of type <span><math><mo>(</mo><mi>m</mi><mo>,</mo><mi>m</mi><mo>,</mo><mi>m</mi><mo>)</mo></math></span> that admit trialities but no dualities. We then prove that they are flag transitive when <span><math><mi>m</mi><mo>=</mo><mn>5</mn></math></span>, no matter the value of <em>q</em>. These geometries form the first infinite family of incidence geometries of rank 3 that are flag transitive and have trialities but no dualities. They are constructed using chamber systems and the trialities come from field automorphisms. These same geometries can also be considered as regular hypermaps with automorphism group <span><math><mi>S</mi><mi>z</mi><mo>(</mo><mi>q</mi><mo>)</mo></math></span>.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106033"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106021
Ming Liu, Houyi Yu
Separable elements in Weyl groups are generalizations of the well-known class of separable permutations in symmetric groups. Gaetz and Gao showed that for any pair of subsets of the symmetric group , the multiplication map is a splitting (i.e., a length-additive bijection) of if and only if X is the generalized quotient of Y and Y is a principal lower order ideal in the right weak order generated by a separable element. They conjectured this result can be extended to all finite Weyl groups. In this paper, we classify all separable and minimal non-separable signed permutations in terms of forbidden patterns and confirm the conjecture of Gaetz and Gao for Weyl groups of type B.
{"title":"Separable elements and splittings in Weyl groups of type B","authors":"Ming Liu, Houyi Yu","doi":"10.1016/j.jcta.2025.106021","DOIUrl":"10.1016/j.jcta.2025.106021","url":null,"abstract":"<div><div>Separable elements in Weyl groups are generalizations of the well-known class of separable permutations in symmetric groups. Gaetz and Gao showed that for any pair <span><math><mo>(</mo><mi>X</mi><mo>,</mo><mi>Y</mi><mo>)</mo></math></span> of subsets of the symmetric group <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>, the multiplication map <span><math><mi>X</mi><mo>×</mo><mi>Y</mi><mo>→</mo><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> is a splitting (i.e., a length-additive bijection) of <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> if and only if <em>X</em> is the generalized quotient of <em>Y</em> and <em>Y</em> is a principal lower order ideal in the right weak order generated by a separable element. They conjectured this result can be extended to all finite Weyl groups. In this paper, we classify all separable and minimal non-separable signed permutations in terms of forbidden patterns and confirm the conjecture of Gaetz and Gao for Weyl groups of type <em>B</em>.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"214 ","pages":"Article 106021"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106032
Y.H. Chen, Thomas Y. He
Bressoud introduced the partition function , which counts the number of partitions with certain difference conditions. Bressoud posed a conjecture on the generating function for the partition function in multi-summation form. In this article, we introduce a bijection related to Bressoud's conjecture. As an application, we give the proof of a companion to the Göllnitz-Gordon identities.
{"title":"A bijection related to Bressoud's conjecture","authors":"Y.H. Chen, Thomas Y. He","doi":"10.1016/j.jcta.2025.106032","DOIUrl":"10.1016/j.jcta.2025.106032","url":null,"abstract":"<div><div>Bressoud introduced the partition function <span><math><mi>B</mi><mo>(</mo><msub><mrow><mi>α</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>α</mi></mrow><mrow><mi>λ</mi></mrow></msub><mo>;</mo><mi>η</mi><mo>,</mo><mi>k</mi><mo>,</mo><mi>r</mi><mo>;</mo><mi>n</mi><mo>)</mo></math></span>, which counts the number of partitions with certain difference conditions. Bressoud posed a conjecture on the generating function for the partition function <span><math><mi>B</mi><mo>(</mo><msub><mrow><mi>α</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><mo>…</mo><mo>,</mo><msub><mrow><mi>α</mi></mrow><mrow><mi>λ</mi></mrow></msub><mo>;</mo><mi>η</mi><mo>,</mo><mi>k</mi><mo>,</mo><mi>r</mi><mo>;</mo><mi>n</mi><mo>)</mo></math></span> in multi-summation form. In this article, we introduce a bijection related to Bressoud's conjecture. As an application, we give the proof of a companion to the Göllnitz-Gordon identities.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"214 ","pages":"Article 106032"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106025
Eiichi Bannai , Hirotake Kurihara , Da Zhao , Yan Zhu
The classification problem of P- and Q-polynomial association schemes has been one of the central problems in algebraic combinatorics. Generalizing the concept of P- and Q-polynomial association schemes to multivariate cases, namely to consider higher rank P- and Q-polynomial association schemes, has been tried by some authors, but it seems that so far there were neither very well-established definitions nor results. Very recently, Bernard, Crampé, d'Andecy, Vinet, and Zaimi [4], defined bivariate P-polynomial association schemes, as well as bivariate Q-polynomial association schemes. In this paper, we study these concepts and propose a new modified definition concerning a general monomial order, which is more general and more natural and also easy to handle. We prove that there are many interesting families of examples of multivariate P- and/or Q-polynomial association schemes.
{"title":"Multivariate P- and/or Q-polynomial association schemes","authors":"Eiichi Bannai , Hirotake Kurihara , Da Zhao , Yan Zhu","doi":"10.1016/j.jcta.2025.106025","DOIUrl":"10.1016/j.jcta.2025.106025","url":null,"abstract":"<div><div>The classification problem of <em>P</em>- and <em>Q</em>-polynomial association schemes has been one of the central problems in algebraic combinatorics. Generalizing the concept of <em>P</em>- and <em>Q</em>-polynomial association schemes to multivariate cases, namely to consider higher rank <em>P</em>- and <em>Q</em>-polynomial association schemes, has been tried by some authors, but it seems that so far there were neither very well-established definitions nor results. Very recently, Bernard, Crampé, d'Andecy, Vinet, and Zaimi <span><span>[4]</span></span>, defined bivariate <em>P</em>-polynomial association schemes, as well as bivariate <em>Q</em>-polynomial association schemes. In this paper, we study these concepts and propose a new modified definition concerning a general monomial order, which is more general and more natural and also easy to handle. We prove that there are many interesting families of examples of multivariate <em>P</em>- and/or <em>Q</em>-polynomial association schemes.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106025"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106030
Peer Stelldinger
De Bruijn tori, or perfect maps, are two-dimensional periodic arrays of letters from a finite alphabet, where each possible pattern of shape appears exactly once in a single period. While the existence of certain de Bruijn tori, such as square tori with odd and even alphabet sizes, remains unresolved, sub-perfect maps are often sufficient in applications like positional coding. These maps capture a large number of patterns, with each appearing at most once. While previous methods for generating such sub-perfect maps cover only a fraction of the possible patterns, we present a construction method for generating almost perfect maps for arbitrary pattern shapes and arbitrary non-prime alphabet sizes, including the above mentioned square tori with odd as long that the alphabet size is non-prime. This is achieved through the introduction of de Bruijn rings, a minimal-height sub-perfect map and a formalization of the concept of families of almost perfect maps. The generated sub-perfect maps are easily decodable which makes them perfectly suitable for positional coding applications.
De Bruijn tori,或完美映射,是有限字母表中字母的二维周期性数组,其中每种可能的形状模式(m,n)在单个周期内恰好出现一次。虽然某些de Bruijn环面(例如奇数m=n∈{3,5,7}和偶数字母大小的平方环面)的存在性仍未得到解决,但在位置编码等应用中,次完美映射通常是足够的。这些地图捕获了大量的模式,每种模式最多出现一次。虽然以前生成这种次完美映射的方法只覆盖了可能模式的一小部分,但我们提出了一种生成任意模式形状和任意非素数字母表大小的几乎完美映射的构造方法,包括上面提到的奇数m=n∈{3,5,7}的方形环面,只要字母表大小是非素数。这是通过引入de Bruijn环,一个最小高度的次完美地图和几乎完美地图族概念的形式化来实现的。生成的次完美地图很容易解码,这使得它们非常适合位置编码应用。
{"title":"On de Bruijn rings and families of almost perfect maps","authors":"Peer Stelldinger","doi":"10.1016/j.jcta.2025.106030","DOIUrl":"10.1016/j.jcta.2025.106030","url":null,"abstract":"<div><div>De Bruijn tori, or perfect maps, are two-dimensional periodic arrays of letters from a finite alphabet, where each possible pattern of shape <span><math><mo>(</mo><mi>m</mi><mo>,</mo><mi>n</mi><mo>)</mo></math></span> appears exactly once in a single period. While the existence of certain de Bruijn tori, such as square tori with odd <span><math><mi>m</mi><mo>=</mo><mi>n</mi><mo>∈</mo><mo>{</mo><mn>3</mn><mo>,</mo><mn>5</mn><mo>,</mo><mn>7</mn><mo>}</mo></math></span> and even alphabet sizes, remains unresolved, sub-perfect maps are often sufficient in applications like positional coding. These maps capture a large number of patterns, with each appearing at most once. While previous methods for generating such sub-perfect maps cover only a fraction of the possible patterns, we present a construction method for generating almost perfect maps for arbitrary pattern shapes and arbitrary non-prime alphabet sizes, including the above mentioned square tori with odd <span><math><mi>m</mi><mo>=</mo><mi>n</mi><mo>∈</mo><mo>{</mo><mn>3</mn><mo>,</mo><mn>5</mn><mo>,</mo><mn>7</mn><mo>}</mo></math></span> as long that the alphabet size is non-prime. This is achieved through the introduction of de Bruijn rings, a minimal-height sub-perfect map and a formalization of the concept of families of almost perfect maps. The generated sub-perfect maps are easily decodable which makes them perfectly suitable for positional coding applications.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"214 ","pages":"Article 106030"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-27DOI: 10.1016/j.jcta.2025.106028
Hau-Wen Huang
<div><div>The Clebsch–Gordan coefficients of <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span> are expressible in terms of Hahn polynomials. The phenomenon can be explained by an algebra homomorphism ♮ from the universal Hahn algebra <span><math><mi>H</mi></math></span> into <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>. Let Ω denote a finite set of size <em>D</em> and <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></math></span> denote the power set of Ω. It is generally known that <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> supports a <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module. Let <em>k</em> denote an integer with <span><math><mn>0</mn><mo>≤</mo><mi>k</mi><mo>≤</mo><mi>D</mi></math></span> and fix a <em>k</em>-element subset <span><math><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> of Ω. By identifying <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> with <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi><mo>∖</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup></mrow></msup><mo>⊗</mo><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup></mrow></msup></math></span> this induces a <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module structure on <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> denoted by <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></math></span>. Pulling back via ♮ the <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></math></span> forms an <span><math><mi>H</mi></math></span>-module. When <span><math><mn>1</mn><mo>≤</mo><mi>k</mi><mo>≤</mo><mi>D</mi><mo>−</mo><mn>1
{"title":"An imperceptible connection between the Clebsch–Gordan coefficients of Uq(sl2) and the Terwilliger algebras of Grassmann graphs","authors":"Hau-Wen Huang","doi":"10.1016/j.jcta.2025.106028","DOIUrl":"10.1016/j.jcta.2025.106028","url":null,"abstract":"<div><div>The Clebsch–Gordan coefficients of <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span> are expressible in terms of Hahn polynomials. The phenomenon can be explained by an algebra homomorphism ♮ from the universal Hahn algebra <span><math><mi>H</mi></math></span> into <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>. Let Ω denote a finite set of size <em>D</em> and <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></math></span> denote the power set of Ω. It is generally known that <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> supports a <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module. Let <em>k</em> denote an integer with <span><math><mn>0</mn><mo>≤</mo><mi>k</mi><mo>≤</mo><mi>D</mi></math></span> and fix a <em>k</em>-element subset <span><math><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> of Ω. By identifying <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> with <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi><mo>∖</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup></mrow></msup><mo>⊗</mo><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup></mrow></msup></math></span> this induces a <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module structure on <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup></math></span> denoted by <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></math></span>. Pulling back via ♮ the <span><math><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo><mo>⊗</mo><mi>U</mi><mo>(</mo><msub><mrow><mi>sl</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span>-module <span><math><msup><mrow><mi>C</mi></mrow><mrow><msup><mrow><mn>2</mn></mrow><mrow><mi>Ω</mi></mrow></msup></mrow></msup><mo>(</mo><msub><mrow><mi>x</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></math></span> forms an <span><math><mi>H</mi></math></span>-module. When <span><math><mn>1</mn><mo>≤</mo><mi>k</mi><mo>≤</mo><mi>D</mi><mo>−</mo><mn>1","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"214 ","pages":"Article 106028"},"PeriodicalIF":0.9,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-26DOI: 10.1016/j.jcta.2025.106031
Tian Yao , Dehai Liu , Kaishun Wang
Let V be a finite dimensional vector space over a finite field. Suppose that , , …, are r-cross t-intersecting families of k-subspaces of V. In this paper, we determine the extremal structure when is maximum under the condition that for each i.
{"title":"More on r-cross t-intersecting families for vector spaces","authors":"Tian Yao , Dehai Liu , Kaishun Wang","doi":"10.1016/j.jcta.2025.106031","DOIUrl":"10.1016/j.jcta.2025.106031","url":null,"abstract":"<div><div>Let <em>V</em> be a finite dimensional vector space over a finite field. Suppose that <span><math><msub><mrow><mi>F</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>, <span><math><msub><mrow><mi>F</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, …, <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>r</mi></mrow></msub></math></span> are <em>r</em>-cross <em>t</em>-intersecting families of <em>k</em>-subspaces of <em>V</em>. In this paper, we determine the extremal structure when <span><math><msubsup><mrow><mo>∏</mo></mrow><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>r</mi></mrow></msubsup><mo>|</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>|</mo></math></span> is maximum under the condition that <span><math><mi>dim</mi><mo></mo><mo>(</mo><msub><mrow><mo>⋂</mo></mrow><mrow><mi>F</mi><mo>∈</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msub><mi>F</mi><mo>)</mo><mo><</mo><mi>t</mi></math></span> for each <em>i</em>.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106031"},"PeriodicalIF":0.9,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-25DOI: 10.1016/j.jcta.2025.106029
Maarten De Boeck , Jozefien D'haeseleer , Morgan Rodgers
Cameron-Liebler sets of generators in polar spaces were introduced a few years ago as natural generalisations of the Cameron-Liebler sets of subspaces in projective spaces. In this article we present the first two constructions of non-trivial Cameron-Liebler sets of generators in polar spaces. Also regular m-ovoids of k-spaces are introduced as a generalization of m-ovoids of polar spaces. They are used in one of the aforementioned constructions of Cameron-Liebler sets.
极空间中的卡梅隆-利伯勒生成器集是几年前作为投影空间中子空间的卡梅隆-利伯勒集的自然广义而提出的。在这篇文章中,我们首次提出了极空间中非难卡梅隆-利伯勒生成器集的两个构造。此外,还介绍了 k 空间的正则 m-ovoids 作为极空间 m-ovoids 的广义。它们被用于上述卡梅隆-利伯勒集合的一个构造中。
{"title":"Regular ovoids and Cameron-Liebler sets of generators in polar spaces","authors":"Maarten De Boeck , Jozefien D'haeseleer , Morgan Rodgers","doi":"10.1016/j.jcta.2025.106029","DOIUrl":"10.1016/j.jcta.2025.106029","url":null,"abstract":"<div><div>Cameron-Liebler sets of generators in polar spaces were introduced a few years ago as natural generalisations of the Cameron-Liebler sets of subspaces in projective spaces. In this article we present the first two constructions of non-trivial Cameron-Liebler sets of generators in polar spaces. Also regular <em>m</em>-ovoids of <em>k</em>-spaces are introduced as a generalization of <em>m</em>-ovoids of polar spaces. They are used in one of the aforementioned constructions of Cameron-Liebler sets.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106029"},"PeriodicalIF":0.9,"publicationDate":"2025-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143480765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-24DOI: 10.1016/j.jcta.2025.106020
Mircea Merca
In 1920, Percy Alexander MacMahon defined the partition generating functions and which have since played an important rol
1920 年,珀西-亚历山大-麦克马洪定义了分区生成函数 Ak(q):=∑0<n1<n2<⋯<nkqn1+n2+⋯+nk(1-qn1)2(1-qn2)2⋯(1-qnk)2 和 Ck(q):=∑0<n1<n2<⋯<nkq2n1+2n2+⋯+2nk-k(1-q2n1-1)2(1-q2n2-1)2⋯(1-q2nk-1)2,它们在组合数学中发挥了重要作用。对于每一个非负整数 k,乔治-安德鲁斯(George E. Andrews)和西蒙-罗斯(Simon C. F. Rose)证明了 Ak(q)可以用分区的生成函数来表示,其中每一部分可以用三种不同颜色中的一种来着色,而 Ck(q)可以用过分区的生成函数来表示。最近,对于每个非负整数 k,Ken Ono 和 Ajit Singh 证明了 Ak(q)、Ak+1(q)、Ak+2(q)......给出了每个部分可以用三种不同颜色中的一种着色的 n 的分区数的生成函数,而 Ck(q)、Ck+1(q)、Ck+2(q)......给出了 n 的过度分区数的生成函数。本文还介绍了一些悬而未决的问题。
{"title":"Truncated forms of MacMahon's q-series","authors":"Mircea Merca","doi":"10.1016/j.jcta.2025.106020","DOIUrl":"10.1016/j.jcta.2025.106020","url":null,"abstract":"<div><div>In 1920, Percy Alexander MacMahon defined the partition generating functions<span><span><span><math><mrow><msub><mrow><mi>A</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><mi>q</mi><mo>)</mo><mo>:</mo><mo>=</mo><munder><mo>∑</mo><mrow><mn>0</mn><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub><mo><</mo><mo>⋯</mo><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub></mrow></munder><mfrac><mrow><msup><mrow><mi>q</mi></mrow><mrow><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub></mrow></msup></mrow><mrow><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><mo>⋯</mo><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac></mrow></math></span></span></span> and<span><span><span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><mi>q</mi><mo>)</mo><mo>:</mo><mo>=</mo><munder><mo>∑</mo><mrow><mn>0</mn><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub><mo><</mo><mo>⋯</mo><mo><</mo><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub></mrow></munder><mfrac><mrow><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>+</mo><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>+</mo><mo>⋯</mo><mo>+</mo><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>−</mo><mi>k</mi></mrow></msup></mrow><mrow><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>−</mo><mn>1</mn></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>−</mo><mn>1</mn></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><mo>⋯</mo><msup><mrow><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn><msub><mrow><mi>n</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>−</mo><mn>1</mn></mrow></msup><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup></mrow></mfrac></math></span></span></span> which have since played an important rol","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106020"},"PeriodicalIF":0.9,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143480764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-24DOI: 10.1016/j.jcta.2025.106022
Valentina Kiritchenko
We construct simple geometric operations on faces of the Cayley sum of two polytopes. These operations can be thought of as convex geometric counterparts of divided difference operators in Schubert calculus. We show that these operations give a uniform construction of Knutson–Miller mitosis in the type A and Fujita mitosis in the type C on Kogan faces of Gelfand–Zetlin polytopes.
{"title":"Simple geometric mitosis","authors":"Valentina Kiritchenko","doi":"10.1016/j.jcta.2025.106022","DOIUrl":"10.1016/j.jcta.2025.106022","url":null,"abstract":"<div><div>We construct simple geometric operations on faces of the Cayley sum of two polytopes. These operations can be thought of as convex geometric counterparts of divided difference operators in Schubert calculus. We show that these operations give a uniform construction of Knutson–Miller mitosis in the type <em>A</em> and Fujita mitosis in the type <em>C</em> on Kogan faces of Gelfand–Zetlin polytopes.</div></div>","PeriodicalId":50230,"journal":{"name":"Journal of Combinatorial Theory Series A","volume":"213 ","pages":"Article 106022"},"PeriodicalIF":0.9,"publicationDate":"2025-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143474227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}