## 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.
Short talk by Rida-e-Zenab, 7th June 2017.
`Online Ramsey Theory', Matthew Brookes, 21st June 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.
On the Identity Problem for SL2(Z) Paul Bell, 29th November 2017
## Spring 2017/18

The finite basis problem for various monoids of Boolean matrices, Peter Fenner 17th January 2018
Actions of E-dense semigroups and an
application to the discrete log problem , Jim Renshaw, 24th January 2018
Speed talks by Victoria Gould, Scott Carson, Rida Zenab and...?? 14th February 2018
Computing direct products of semigroups W. Wilson, 21st February 2018.
Zero-divisor graphs of MV-algebras Aiping Gan 28th February 2018.
Endomorphisms of the random graph
Martyn Quick, 7th March 2018.
Coherence and Uniform Interpolation
George Metcalfe, 14th March 2018.
## Summer 2017/18

Two ways to generalise inverse semigroups. Tim Stokes, 25th April 2018
Reflection Monoids , Majed Albaity, 2nd May 2018
Some of Douglas Munn's Contributions to
Representation Theory of Semigroups Sanaa Bajri, 9th May 2018
Intersections of Principal Ideals of a Free Monoid
Presentation, Scott Carson, 16th May 2018
Strongly Minimal Semigroups, Charlotte Kesner, 23rd May 2018
Valence automata over E-unitary inverse
semigroups Erszebet Dombi, 30th May 2018
Model theory of finite and pseudofinite groups, Dugald Macpherson, 6th June 2018
## Autumn 2018/19

Restriction and ample semigroups: constructions and Maria Szendrei's work , Victoria Gould, 10th October 2018
Equations in free monoids, formal languages, and complexity , Laura Ciobanu, 17th October 2018
Relational Representation of Semigroups Szabolcs Mikulas, 24th October 2018
Conjugacy in epigroups Antonio Malheiro, 31st October 2018
Speed talks by: Rida-e-Zenab, Matthew Brookes, Lei Sun, Aiping Gan, Victoria Gould, Scott Carson and Georgia Schneider. Comperes: Scott and Matthew.
Transversals as generating sets, Maurice Chiodo, 14th November 2018.
Strange semigroups and their presentations Talks by Scott Carson and Zero-divisor graphs of idealizations with respect to
semimodules over inclines Aiping Gan, 21st November 2018.
Building CSPs from semigroups Thomas Quinn-Gregson, 28th November 2018
## Spring 2018/19

The relationship between coherency and purity for modules and acts, Dandan Yang, 23rd January 2019.
Coverings and embeddings for left restriction monoids, Rida Zenab, 30th January 2019.
Post-quantum (semi)-group-based Cryptography, Delaram Kahrobaie, 6th February 2019.
Word problems and formal language theory, Richard Thomas, 13th February 2019.
Maximal left ideals in Banach algebras Garth Dales, 20th February 2019.
Undecidability of the word problem for
one-relator inverse monoids Robert Gray, 6th March 2019
Inverse monoids and immersions of cell complexes Nora Szakacs, 13th March 2019
## Summer 2018/19

Wagner's theory of generalised heaps, Christopher Hollings, 17th April 2019.
Semigroup identities of tropical matrices, Zur Izhakian, 24th April 2019
The Post Correspondence Problem for free groups, Alan Logan, 1st May 2019
Efficient graph rewriting Graham Campbell, 8th May 2019.
Complexity of positive cones, Yago Antolin, 15th May 2019.
Inverse semigroups of left I-quotients, Georgia Schneider, 22nd May 2019.
Reflexivity and Self-Referentiality
In Inverse Monoids and Categories, Peter Hines, 29th May 2019.
The Howson property for one-sided ideals of
semigroups Scott Carson, Congruences on G wr I_n Matthew Brookes, 5th June 2019
Some semigroup theory on some endomorphism monoids
of relational first-order structures Tom Coleman, 19th June 2019.
Congruences on ideals of semigroups and categories
James East; Tropical Representations of Plactic Monoids, Mark Kambites, 3rd July 2019.
## Autumn 2019/20

Transformation Semigroups and their Automorphisms, Wolfram Bentz, 9th October 2019
Hyperbolic and tree-like inverse monoids, Nora Szakacs, 16th October 2019
Equations and logic on words, Sam van Gool, 22nd October 2019 (an expository talk, background for the YS on the following day).
Pointlike sets for varieties determined by groups, Sam van Gool, 23rd October 2019
Engel conditions in groups of automorphisms of rooted trees, Marialaura Noce, 30th October 2019
Building more automatic structures for groups , Sarah Rees, 6th November 2019
Min network of congruences on an inverse semigroup , Ying-Ying (Ricky) Feng, 13th November 2019.
Speed talks: Scott Carson, Ricky Feng, John Fountain, Matthew Brookes, Nora Szakacs, Victoria Gould, Nouf Alqathani, Georgia Schneider, Ambroise Grau, 27th November 2019.
Degree 2 transformation semigroups as adjoint maps on graphs,
Stuart Margolis, 2nd December 2019
Cell complexes, poset topology and the representation theory of algebras arising in algebraic combinatorics and discrete geometry, Stuart Margolis, 2nd December 2019 (Joint with the Algebra Seminar)