YORK SEMIGROUP

Summer 2009/10

  • Inverse semigroups and inductive groupoids Victoria Gould, 4th May 2010
  • Semigroups of left I-quotients Nassraddin Ghroda, 11th May 2010
  • Symmetric and dual symmetric inverse monoids James East, 20th May 2010
  • Applications of order-preserving partial permutations James East, 21st May 2010
  • Beyond the Ehresmann-Schein-Nambooripad Theorem Christopher Hollings, 25th May 2010
  • Ordered covers Lubna Shaheen, 1st June 2010
  • Structure theorems for weakly B-abundant semigroups Yanhui Wang, 8th June 2010
  • An Introduction to Graph Expansions Claire Cornock, 15th June 2010

    Autumn 2010/11

  • Short presentations by Victoria Gould, Claire Cornock and Lubna Shaheen on: `A note on maximal subgroups of free idempotent generated subsemigroups over bands' by Igor Dolinka arXiv:1010.3737; `Free adequate semigroups' by Mark Kambites arXiv:0902.0927; `Clifford semigroups such that SF is axiomatisable' by Lubna Shaheen, 1st November 2010
  • `The Morita theory of semigroups and applications' Mark Lawson, 8th November 2010
  • Short presentations by Victoria Gould, Lubna Shaheen and Yanhui Wang on: `Numerical Semigroups' by J.C. Rosales and P.A. Garcia-Sanchez, book review by Ralf Froberg, Semigroup Forum 81 (2010), 555-557; `The semigroup generated by certain operators on the congruence lattice of a Clifford semigroup' by M. Petrich, Semigroup Forum 45 (1992), 332-341; `Groupoids and Cayley graphs' by Brian Leary, 15th November 2010
  • `A common framework for restriction semigroups and regular *-semigroups' Peter Jones, 22nd November 2010
  • `The finite F-inverse cover problem' Maria Szendrei, 29th November 2010
  • `Equations defining the polynomial closure of lattice of languages', Mario Branco, 6th December 2010.
  • `Equations defining the polynomial closure of lattice of languages II', Mario Branco, 6th December 2010.

    `Spring' 2010/11

  • Presentation by Victoria Gould on The Knuth-Bendix algorithm and the conjugacy problem in monoids by Fabienne Chouraqui, 9th February 2011
  • `A short history of inverse semigroups' Christopher Hollings (Oxford), 16th February 2011
  • `An introduction to model theory of S-acts and S-posets' Lubna Shaheen, 23rd February 2011
  • Varieties of restriction semigroups Claire Cornock, 2nd March 2011
  • The Thompson group V John Fountain, 9th March 2011
  • Monoids acting by isometric embeddings Mark Kambites (Manchester), 16th March 2011

    `Summer' 2010/11

  • Inverse semigroups acting on graphs and trees Jim Renshaw (Southampton), 12th May 2011
  • Statement calculus; Victoria Gould (York), 18th May 2011
  • Beyond orthodox semigroups, Yanhui Wang (York), 25th May 2011
  • Statement calculus II; Victoria Gould (York), 1st June 2011
  • First order languages and structures; Victoria Gould (York), 8th June 2011
  • Maximal subsemigroups of the semigroup of mappings on an infinite set, James Mitchell (St Andrews), 15th June 2011.
  • Cohomological dimension of inverse semigroups, Nick Gilbert (Heriot-Watt), 22nd June 2011.

    Autumn 2011/12

  • Non-commutative Stone duality, Mark Lawson (Heriot-Watt), October 19th 2011.
  • Ends of Semigroups, Simon Craik (St Andrews), 2nd November 2011.
  • Weakly U-abundant semigroups, Yanhui Wang, 9th November 2011.
  • Restriction and related semigroups, Victoria Gould, 16th November 2011.
  • The kernel of a monoid morphism, Jean-Eric Pin, 24th November 2011.
  • An Introduction to Zappa-Szep Products, Rida-e-Zenab, 7th December 2011.
  • Synchronizing groups and semigroups, Peter Neumann, 14th December 2011.
  • Locally Ehresmann semigroups, Dandan Yang, 21st December 2011.
  • Restriction and related semigroups cont. Victoria Gould, 21st December 2011.

    Spring 2011/12

  • Free idempotent generated semigroups, Dandan Yang, 11th January 2012.
  • Covers of acts over monoids, Alex Bailey (Southampton) 18th January 2012.
  • Independence Algebras, Victoria Gould 25th January 2012.
  • E-unitary and almost factorisable orthodox semigroups, Miklos Hartmann 2nd February 2012.
  • Free idempotent generated semigroups II , Dandan Yang, 9th February 2012.
  • Embeddable E-unitary orthodox semigroups, Miklos Hartmann 15th February 2012.
  • Strongly T-proper left Ehresmann monoids Yanhui Wang, 22nd February 2012.
  • Idempotent tropical matrices Marianne Johnson, 29th February 2012.
  • Burrows-Wheeler transforms and de Bruijn Words, Peter Higgins, 7th March 2012.
  • Short presentations by Victoria Gould, Dandan Yang and Rida Zenab on: `Inverse semigroup expansions and their actions on C^*-algebras' by Alcides Buss and Ruy Exel arXiv:1112.0771v1; `On a problem of M. Kambites regarding abundant semigroups' by Joao Araujo and Michael Kinyon arXiv:1006.3677 and `Malcev products of unipotent monoids and varieties of bands', by Mario Petrich, Semigroup Forum 83 161-189 (2011), 14th March 2012.

    Summer (aka the rainy season) 2011/12

  • Short presentations by Miklos Hartmann and Yanhui Wang, 25th April 2012 `Inverse semigroups of partial automaton permutations' by A. Olijnyk, V. I. Sushchansky and J. K. Slupik, IJAC 20 (2010), 923-952; `On the closure of the extended bicyclic semigroup', by I. Fihel and O. Gutik, arXiv:1201.0090v1.
  • Free idempotent generated semigroups over biordered sets Dandan Yang, 2nd May 2012
  • Zappa-Szep products of groups and semigroups Rida Zenab, 9th May 2012
  • Free idempotent generated semigroups over the full linear monoid Bob Gray (Lisbon) 16th May 2012
  • `Proper restriction semigroups - semidirect products and W-products', Victoria Gould (joint work with Maria Szendrei), 6th June 2012.
  • Semigroup nearrings , John Meldrum (Edinburgh), 13th June 2012.
  • Short presentations by Rida-e-Zenab `Affine semirings having a unique Betti element' P.A. Garcia Sanches, I. Ojeda and J.C. Rosales, arXiv:1203.4138v2 and Dandan Yang `A problem on generalized Cayley graphs of semigroups', Semigroup Forum 2012 DOI: 10.1007/s00233-012-9407, 20th June 2012.

    Autumn 2012/13

  • `Linear' representations of the polycyclic monoids , Miklos Hartmann, 10th October 2012.
  • `The quest for a logic for P', Markus Pfeiffer, 17th October 2012
  • Short presentations by Victoria Gould `The semigroup generated by the idempotents of a partition monoid' by J. East and D. Fitzgerald, J. Algebra 372 (2012), 108-133 and Rida-e-Zenab `A 2-base for inverse semigroups' by J. Araujo and M. Kinyon, arXiv 120.3285v1, 24th October 2012
  • Tara Brough, `Inverse semigroups with rational word problem are finite', 7th November 2012
  • David Wilding, `Matrices over exact semirings', 14th November 2012
  • NBSAN day, 21st November 2012: A Zigzag theorem for partially ordered monoids , Nasir Sohail.
  • Short presentations by Miklos Hartmann `Ascending chain conditions on semidirect products of semigroups', by Nik Stopar Semigroup Forum 85 (2012), 322-336 and Dandan Yang `Ideals and finiteness conditions for subsemigroups' by R. Gray, N. Ruskuc, V. Maltcev and J. Mitchell http://arxiv.org/pdf/1204.6602v1.pdf, 5th December 2012
  • Densely embedded ideals: a handy tool from the pages of Soviet semigroup theory, Chris Hollings, 10th Decemember 2012 (please note non-standard day)

    Spring (aka Winter) 2012/13

  • Monoids acting by isometric embeddings , Mark Kambites, 16th January 2013
  • Hopfian property for semigroups, Nik Ruskuc, 23rd January 2013
  • Subsemigroups of the Full Transformation Monoid on an infinite set , Yann Peresse, 6th February 2013
  • Presentation by Rida-e-Zenab on ``On a topological simple Warne extension of a semigroup'' by Iryna Fihel, Oleg Gutik, Kateryna Pavlyk ArXiv: 1301.1232vI
  • The structure of the monoid associated with a self-similar group action, Mark Lawson, 20th February 2013
  • Partition monoids, Miklos Hartmann, 27th February 2013
  • S-acts, coherency and stability Part I , Victoria Gould, 6th March 2013
  • S-acts, coherency and stability Part II, Victoria Gould, 13th March 2013

    Summer (aka Spring) 2012/13

  • The word problem for a quotient of a free adequate semigroup, Miklos Hartmann, 1st May 2013
  • Free idempotent generated semigroups over bands, Dandan Yang, 8th May 2013
  • Semigroups with skeletons and Zappa-Szep products, Rida-e-Zenab, 9th May 2013
  • The word problem for a quotient of a free adequate semigroup II, Miklos Hartmann, 15th May 2013
  • Categorical and semigroup-theoretic descriptions of Bass-Serre Theory, Mark Lawson, 22nd May 2013
  • Informal talks by Dandan Yang and Rida Zenab, 29th May, 2013
  • Some properties of left and right negatively orderable semigroups, Zsofia Juhasz, 12th June 2013
  • Semigroups of equational classes of functions, Tamas Waldhauser, 19th June 2013

    Autumn 2013/14

  • Injective and bijective globalisability of partial actions, Miklos Hartmann, 2nd October 2013
  • Rewriting systems and partial actions, Miklos Hartmann, 9nd October 2013
  • MacLane's theorem and the Foundations of Category Theory Peter Hines (Computer Science, York), 16th October 2013
  • Informal talks by Victoria Gould (The normal subsemigroups of the monoid of injective maps, M. Droste and R. Gobel, Semigroup Forum 87 (2013), 298-312) and Dandan Yang (Defining relations for idempotent generators in finite partial transformation semigroups, J. East, Semigroup Forum DOI 10.1007/s00233-013-9512-9)
  • Purity for S-acts Victoria Gould, 30th October 2013
  • Reconsidering MacLane (again): algorithms for coherence Peter Hines (Computer Science, York) 6th November 2013
  • Universal algebra for constraint satisfaction Andrei Krokhin (Durham, Computer Science) 13th November 2013
  • 20th November, NBSAN meeting , including the York Semigroup talk `Some monoids and notions of homomorphism-homogeneity' by John Truss.
  • Revisiting automatic semigroups - change of generators , Dr Erzsebet Dombi, 3rd December 2013.
  • Radicals of some semigroup algebras, Garth Dales, 4th December 2013.
  • New developments in the theory of non-commutative Stone duality , Mark Lawson, 16th December 2013.

    Spring 2013/14

  • A representation theorem for independence algebras, Dandan Yang, 7th January 2014.
  • Automorphisms of tropical polytopes, Marianne Johnson, 15th January 2014.
  • Computing a finite semigroup, James Mitchell, 4th February 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 5th February 2014.
  • The finite basis problem for unary matrix semigroups Igor Dolinka, 12th February 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 19th February 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 26th February 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 5th March 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 12th March 2014.

    Summer 2013/14

  • On the Birman-Corran Conjecture, Amelia Gontar, 16th April 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 23rd April 2014.
  • $\aleph_0$-categorical semigroups, Tom Quinn-Gregson, 30th April 2104.
  • Infinite monoids as geometric objects, Robert Gray (University of East Anglia), 7th May 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 14th May 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 21st May 2014.
  • Comparison Semigroups, Tim Stokes, 11th June 2014.
  • The Krohn-Rhodes Theorem, John Fountain, 18th June 2014.
  • The Brauer Project: Enumeration of idempotents in partition monoids , James East, 26th June 2014.
  • Idempotent generators in infinite partition monoids, James East, 4th July 2014.

    Autumn 2014/15

  • Clones determined by clausal relations , Edith Vargas-Garcia, 8th October 2014.
  • Zariski structures of trivial type, Lubna Shaheen, 15th October 2014.
  • Congruences and quotients of inverse semigroups Nick Gilbert, 22nd October 2014.
  • Knot semigroups: a new algbraic approach to knots and braids Alexei Vernitski, 29th October 2014.
  • The solvability of the word problem for automatic semigroups, Miklos Hartmann, 5th November 2014.
  • Classes of Groups with Rational Cross-Section John Fountain, 26th November 2014.
  • Notions of properness for semigroups Victoria Gould, 3rd December 2014.
  • Notions of properness for semigroups continued from last week.... Victoria Gould, 10th December 2014.

    Spring 2014/15

  • Variants of semigroups - the case study of finite full transformation monoids , Igor Dolinka. Igor's talk was part of NBSAN 19
  • An introduction to free idempotent generated semigroups , Victoria Gould, 28th January 2015.
  • Non-commutative geometry, schemes, monoids and their model-theoretic semantics, Boris Zilber, 4th February 2015.
  • Short presentations by Asawer Hamdi (number of idempotents in the endomorphism monoid of a free G-act), Tom Quinn-Gregson (homogeneity for finite nilpotent semigroups), 11th February 2015.
  • Free semigroups, groups, and presentations - a brief introduction. Victoria Gould, 25th February 2015.
  • Sufficient conditions for a group Of homeomorphisms of the Cantor set to be 2-Generated James Hyde, 4th March 2015
  • Games and binary relations, Robin Hirsch, 11th March 2015.

    Summer 2014/15: Page needs completion

  • NBSAN 20 took place in St Andrews, 22nd-23rd April 2015.
  • Endomorphism monoids of countably infinite structures Andras Pongracz, 29th April 2015.
  • Amenability of finitely generated semigroups Mark Kambites, 13th May 2015.

    Autumn 2015/2016: Page needs completion

  • The solution of the generalised Pei Huisheng problem Wolfram Bentz, 4th November 2015.

    Spring 2015/2016

  • Idempotents and partial transformation monoids Yang Dandan (Xidian), 12th January 2016.
  • Almost pure and absolutely pure S-acts Salma Shaheen (Quaid-i-Azam), 19th January 2016.
  • Representations of finite regular semigroups Brent Everitt, 26th January 2016.
  • Representations of finite regular semigroups Brent Everitt, 9th February 2016.
  • An introduction to projective modules and diagram chasing, John Fountain, 16th February 2016.
  • Removal lemmas for multinomials, David Ferguson, 23rd February 2016.
  • New directions in self-similar group theory, Mike Whittaker (Glasgow), 24th February 2016.
  • Completely regular semigroups and (Completely) (E:H~E)-abundant semigroups (a.k.a. U-superabundant semigroups): Similarities and Contrasts Xavier Mary (Paris 10), 2nd March 2016.
  • Representations of finite regular semigroups Brent Everitt, 8th March 2016.

    Summer 2015/2016

  • Two kinds of congruence networks on regular semigroups Ying-Ying (Ricky) Feng, 20th April 2016.
  • Representations of finite regular semigroups Brent Everitt, 4th May 2016.
  • NBSAN 24 Garth Dales, Dona Strauss, Catarina Santa-Clara, Bob Gray, Chris Hollings and Mark Kambites, 11th May 2016
  • Representations of finite regular semigroups Brent Everitt, 18th May 2016.
  • Homogeneous bands Tom Quinn-Gregson, 25th May 2016.
  • Counting idempotents in semigroups of partitions James Mitchell, 1st June 2016.
  • Representations of finite regular semigroups Brent Everitt, 7th June 2016.
  • Motzkin monoids James East, 5th August 2016.

    Autumn 2016/2017

  • Subwords and Stars Tom Bourne, 5th October 2016.
  • Partial semigroups: categories and constellations Victoria Gould, 12th October 2016.
  • On combinatorial conditions determining isomorphism class for finitely generated subgroups of Homeo_+(I): Advanced Ping-Pong dynamics, Collin Bleak, 19th October 2016.
  • A Fraisse-like theorem for homomorphism-homogeneous structures, Tom Coleman, 26th October 2016.
  • Finitely Generated Left Ideals in Banach Algebras on Monoids, Jared White, 2nd November 2016.
  • Semigroups from digraphs Maximilien Gadouleau, 9th November 2016.
  • Infinite rewriting systems in monoids and groups, Andrew Duncan, 23rd November 2016.
  • Tropical algebra, Munazza Naz, 30th November 2016.

    Spring 2016/17

  • Galois and his groups, Peter Neumann, 18th January 2017.
  • Cayley automatic semigroups Rick Thomas, 25th January 2017.
  • Presentations of idempotent generated semigroups, Asawer Hamdi, 1st February 2017.
  • Congruence lattices of partition monoids Nik Ruskuc, 8th February 2017.
  • Monoids, S-acts and coherency Victoria Gould, 22nd February 2017.
  • Knot semigroups, their cousins (keis, quandles and groups), proved results and new conjectures Alexei Vernitski, 8th March 2017.
  • Monoids, S-acts and coherency cont., Victoria Gould, 15th March 2017.

    Summer 2016/17

  • Generating sets for powers of finite algebras and the complexity of quantified constraints Barnaby Martin, 3rd May 2017.
  • Some novel semigroup topics, Peter Higgins, 10th May 2017.
  • Identities in upper triangular matrix semigroups and the bicyclic monoid, Marianne Johnson, 17th May 2017.
  • Short talks by Victoria Gould on `Zappa-Szep product groupoids and C^*-blends' (N.Brownlowe, D. Pask, J. Ramagge, D. Robertson and M. F. Whittaker) and Tom Quinn-Gregson on `Universal locally finite maximally homogeneous semigroups and inverse semigroups' (I. Dolinka and B. Gray), 31st May 2017.

    Autumn 2017/18

  • Introduction by Victoria Gould and Tom Quinn-Gregson, 4th October 2017
  • Short talks by Tom Quinn-Gregson (B.Khosravi, Semigroup Forum, ...) and Philip Hutchinson (Constellations, based on ....) , 11th October 2017
  • `Topologies on the Full Transformation Monoid', Yann Peresse, 18th October 2017
  • `Automatic homeomorphicity of some monoids derived from the rationals, John Truss, 25th October 2017
  • `The Flow Transformation Semigroup of a Digraph, a Complete Invariant for Finite Graphs: Solution to a Conjecture of Rhodes on its Maximal Subgroups and Krohn-Rhodes Complexity, and Relations to Biological Computation', Chrystopher Nehaniv, 1st November 2017
  • `Computing with transformations: groups and semigroups', Markus Pfeiffer, 8th November 2017
  • 14th November 2017 (note non standard day) James Mitchell
  • 22nd November 2017 Short talks by Matthew Brookes, Munazza Naz.
  • 29th November 2017 Paul Bell