Centre for Interdisciplinary Research in Computational Algebra (CIRCA): Recent submissions

Now showing items 16-20 of 22

    • Green index in semigroups : generators, presentations and automatic structures 

      Cain, A.J.; Gray, R; Ruskuc, Nik (2012) - Journal article
      The Green index of a subsemigroup T of a semigroup S is given by counting strong orbits in the complement S n T under the natural actions of T on S via right and left multiplication. This partitions the complement S nT ...

    • Unary FA-presentable semigroups 

      Cain, Alan James; Ruskuc, Nik; Thomas, R.M. (2012-06-08) - Journal article
      Automatic presentations, also called FA-presentations, were introduced to extend nite model theory to innite structures whilst retaining the solubility of interesting decision problems. A particular focus of research has ...

    • Growth rates for subclasses of Av(321) 

      Albert, M.H.; Atkinson, M.D.; Brignall, R; Ruskuc, Nik; Smith, R; West, J (2010-10-22) - Journal article
      Pattern classes which avoid 321 and other patterns are shown to have the same growth rates as similar (but strictly larger) classes obtained by adding articulation points to any or all of the other patterns. The method of ...

    • Generators and relations for subsemigroups via boundaries in Cayley graphs 

      Gray, R; Ruskuc, Nik (2011-11) - Journal article
      Given a finitely generated semigroup S and subsemigroup T of S we define the notion of the boundary of T in S which, intuitively, describes the position of T inside the left and right Cayley graphs of S. We prove that if ...

    • Finite groups are big as semigroups 

      Dolinka, Igor; Ruskuc, Nik (2011-09) - Journal article
      We prove that a finite group G occurs as a maximal proper subsemigroup of an infinite semigroup (in the terminology of Freese, Ježek, and Nation, G is a big semigroup) if and only if |G| ≥ 3. In fact, any finite semigroup ...