Ara es mostren els items 1-20 de 125

    • A list of applications of stallings automata 

      Delgado Pin, Jordi; Ventura Capell, Enric (2022-11-22)
      Article
      Accés obert
      This survey is intended to be a fast (and reasonably updated) reference for the theory of Stallings automata and its applications to the study of subgroups of the free group, with the main accent on algorithmic aspects. ...
    • A polynomial-time reduction from the multi-graph isomorphism problem to additive codeequivalence 

      Ball, Simeon Michael; Dixon, James (2021-12-02)
      Article
      Accés obert
      We present a polynomial-time reduction from the multi-graph isomorphism problem to the problem of code equivalence of additive codes over finite extensions of the field with two elements.
    • A rainbow Dirac's theorem 

      Coulson, Matthew John; Perarnau Llobet, Guillem (2020-01-01)
      Article
      Accés obert
      A famous theorem of Dirac states that any graph on n vertices with minimum degree at least n/2 has a Hamilton cycle. Such graphs are called Dirac graphs. Strengthening this result, we show the existence of rainbow Hamilton ...
    • A removal lemma for systems of linear equations over finite fields 

      Král, Daniel; Serra Albó, Oriol; Vena Cros, Lluís (2012-01)
      Article
      Accés obert
      We prove a removal lemma for systems of linear equations over finite fields: let X1, . . . , Xm be subsets of the finite field Fq and let A be a (k × m) matrix with coefficients in Fq and rank k; if the linear system Ax = ...
    • A step beyond Freiman’s theorem for set addition modulo a prime 

      Candela Pokorna, Pablo; Serra Albó, Oriol; Spiegel, Christoph (2020-01-01)
      Article
      Accés obert
      Freiman’s 2.4-Theorem states that any set A¿Zp satisfying |2A|=2.4|A|-3 and |A|<p/35 can be covered by an arithmetic progression of length at most |2A|-|A|+1. A more general result of Green and Ruzsa implies that this ...
    • Acyclic edge colourings of graphs with large girth 

      Cai, Xing Shi; Perarnau Llobet, Guillem; Reed, Bruce; Watts, Adam Bene (2016-11-03)
      Article
      Accés obert
      An edge colouring of a graph G is called acyclic if it is proper and every cycle contains at least three colours. We show that for every e > 0, there exists a g = g(e) such that if G has maximum degree ¿ and girth at least ...
    • Additive MDS codes 

      Ball, Simeon Michael; Adriaensen, Sam (2022)
      Text en actes de congrés
      Accés obert
      We prove that an additive code over a finite field which has a few projections which are equivalent to a linear code is itself equivalent to a linear code, providing the code is not too short.
    • Additive volume of sets contained in few arithmetic progressions 

      Freiman, Gregory A.; Serra Albó, Oriol; Spiegel, Christoph (De Gruyter, 2019-03-06)
      Article
      Accés obert
      A conjecture of Freiman gives an exact formula for the largest volume of a finite set A of integers with given cardinality k=|A| and doubling T=|2A|. The formula is known to hold when T=3k-4, for some small range over 3k-4 ...
    • An approximate structure theorem for small sumsets 

      Campos, Marcelo; Coulson, Matthew John; Serra Albó, Oriol; Wötzel, Maximilian (Birkhäuser, 2021-08-24)
      Capítol de llibre
      Accés obert
      Let A and B be randomly chosen s-subsets of the first n integers such that their sumset A+B has size at most Ks. We show that asymptotically almost surely A and B are almost fully contained in arithmetic progressions PA ...
    • An Erdös–Fuchs theorem for ordered representation functions 

      Cao Labora, Gonzalo; Rué Perna, Juan José; Spiegel, Christoph (2020-10-28)
      Article
      Accés obert
      Letk=2 be a positive integer. We study concentration results for the ordered representationfunctionsr=k(A, n) = #{(a1= ··· =ak)¿ Ak:a1+···+ak=n}andr<k(A, n) = #{(a1<···<ak)¿ Ak:a1+···+ak=n}for any infinite set ...
    • An irrational-slope Thompson’s group 

      Burillo Puig, José; Nucinkis, Brita; Reeves, Lawrence (2021-01-01)
      Article
      Accés obert
      The purpose of this paper is to study the properties of the irrational-slope Thompson’s group Ft introduced by Cleary in [11]. We construct presentations, both finite and infinite, and we describe its combinatorial structure ...
    • Approximation and decomposition in lattices of clutters 

      Martí Farré, Jaume; Mier Vinué, Anna de (2023-08-01)
      Article
      Accés obert
      A clutter on O is a family of subsets of O that are incomparable under inclusion. Given a collection S of clutters on O and another clutter ¿ on O, we study the problem of approximating and decomposing ¿ in terms of the ...
    • Arcs and tensors 

      Ball, Simeon Michael; Lavrauw, Michel (2019-08-01)
      Article
      Accés obert
      To an arc A of PG(k-1,q) of size q+k-1-t we associate a tensor in ¿¿k,t(A)¿¿k-1 , where ¿k,t denotes the Veronese map of degree t defined on PG(k-1,q) . As a corollary we prove that for each arc A in PG(k-1,q) of size ...
    • Arcs in finite projective spaces 

      Ball, Simeon Michael; Lavrauw, Michel (2019-11-23)
      Article
      Accés restringit per política de l'editorial
      This is an expository article detailing results concerning large arcs in finite projective spaces. It is not strictly a survey but attempts to cover the most relevant results on arcs, simplifying and unifying proofs of ...
    • Asymptotics of sequences 

      Bender, Edward; Rué Perna, Juan José (2017-12-01)
      Capítol de llibre
      Accés restringit per política de l'editorial
    • Autòmats de Stallings, un camí d'anada i tornada 

      Ventura Capell, Enric; Delgado Rodríguez, Jordi (2022-12-14)
      Article
      Accés obert
      En aquest article revisem algunes de les propietats fonamentals del grup lliure i fem una exposició detallada de la teoria dels autòmats de Stallings, una interpretació geomètrica dels seus subgrups que ha estat (i segueix ...
    • Big Ramsey degrees of 3-uniform hypergraphs 

      Balko, Martin; Chodounsky, David; Hubicka, Jan; Konecny, Matej; Vena Cros, Lluís (2019)
      Text en actes de congrés
      Accés obert
      Given a countably infinite hypergraph $\mathcal R$ and a finite hypergraph $\mathcal A$, the \emph{big Ramsey degree} of $\mathcal A$ in $\mathcal R$ isthe least number $L$ such that, for every finite $k$ and every ...
    • Caracteritzant els codis de Gauss: només cal girar la cantonada 

      Vena Cros, Lluís (2020-02-05)
      Article
      Accés obert
      Aquest document està dedicat a la història, les motivacions i algunes solu-cions alproblema dels codis de Gauss.Una corba tancada al pla pot contenir punts d’autointersecció; en suposem unnombre finit, suposem els talls ...
    • Chordal graphs with bounded tree-width 

      Castellví Foguet, Jordi; Drmota, Michael; Noy Serrano, Marcos; Requile, Clement (Masaryk University, 2023)
      Comunicació de congrés
      Accés obert
      Given $t\ge 2$ and $0\le k\le t$, we prove that the number of labelled $k$-connected chordal graphs with $n$ vertices and tree-width at most $t$ is asymptotically $c n^{-5/2} \gamma^n n!$, as $n\to\infty$, for some constants ...
    • Commutators in groups of piecewise projective homeomorphisms 

      Burillo Puig, José; Lodha, Yash; Reeves, Lawrence (2018-07-09)
      Article
      Accés obert
      In [7] Monod introduced examples of groups of piecewise projective homeomorphisms which are not amenable and which do not contain free subgroups, and in [6] Lodha and Moore introduced examples of finitely presented groups ...