Due to the severity of the coronavirus pandemic, we unfortunately have to postpone the workshop.
A new date will be set once we have a clearer idea about how long the current measures last.
We apologize for any inconvenience.

The aim of the workshop is to give an accessible exposition of the recent developments regarding geometric methods in semigroup theory, as well as some of the interplay between semigroups, geometric group theory and C*-algebras.

The use of geometric methods in group theory, in particular the investigation of geometric/topological properties of metric spaces naturally associated to groups has proven to be a very successful approach. Motivated by this, in the past couple of decades adventurous semigroup theorists and geometric group theorists have teamed up to develop similar methods for larger classes of semigroups. This has resulted in interesting and deep theories, including (but not limited to):

Some of the ideas developed for semigroups in turn yield new results in geometric group theory, such as a generalization of the Švarc-Milnor lemma, finding RAAGs in one-relator groups, or various  results about the submonoid membership problem in groups. Semigroups also come up naturally in the definition of near group actions.

At the same time, certain aspects of geometric (semi)group theory have come up in the study of C*-algebras. One way the three fields connect is through self-similarity. On the one hand, self-similar structures naturally give rise to inverse semigroups of isomorphisms between their substructures of different scales, whereas self-similar groups are one of the key objects of geometric group theory. Nekrashevych introduced C*-algebras associated to self-similar groups, which was also described as the universal C*-algebra for tight representations of an associated inverse semigroup. This inverse semigroup is exactly the inverse hull of the Zappa-Szép product of a free monoid and the group.
C*-algebras have also motivated the study of the amenability of inverse  semigroups.


Yves de Cornulier (CNRS, University Lyon 1, FRA)
James East (Western Sydney University, AUS)
Brent Everitt (University of York, UK)
Martin Finn-Sell (University of Vienna, AUT)
Albert Garreta (University of the Basque Country, ESP)
Alejandra Garrido (University of Newcastle, AUS)
Robert Gray (University of East Anglia, UK)
Mark Kambites (University of Manchester, UK)

Nadia Larsen (University of Oslo, NOR)
Mark Lawson (Heriot-Watt University, UK)
John Meakin (University of Nebraska-Lincoln, USA)
Diego Martínez (ICMAT - Institute of Mathematical Sciences, ESP)
Charles Starling* (Carleton University, CAN)
Benjamin Steinberg (City College of New York, USA)
Nóra Szakács (University of York, UK)

*to be confirmed

The workshop is organized by Nóra Szakács, and is funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 799419.


Talks will start on the morning of June 17th and will finish in the late afternoon of June 19th.
The program will include a conference dinner on the 18th at Carluccio's.

More details coming later.


The workshop will be held in the King's Manor (map) located in the center of York – a lively English city roughly halfway between London and Edinburgh with a large gothic cathedral, a nearly complete medieval city wall, and many pubs and restaurants.

Getting to York

By plane: the closest airports to York are in Leeds (LBA), Doncaster (DSA) and Manchester (MAN). Out of the three, Manchester is often the most convenient as it has direct flights to many countries, and direct trains from the airport to York. From Leeds and Doncaster, you first take a bus to the railway station and then the train, but the train tickets can be cheaper than from Manchester.

By train: there is only one railway station in York, so you cannot miss it. One can buy train tickets online on websites like Trainline. There are tickets valid for specific trains only, tickets valid for any train on a given day, or any train at all. The ones for specific trains are cheaper but are non-refundable, and their prices are constantly changing based on market response (like plane tickets), so it is generally a good idea to book them a few weeks in advance. Anytime day tickets have fixed prices. Be aware that from Manchester Airport the tickets for specific trains are valid for another 3 hours, however you cannot buy them on the same day.


York gets very touristic during the summer, so we recommend that you book your accommodation as soon as possible. We have reserved a limited number of studio apartments at Staycity Aparthotels for 14-19 June, which are available for participants at the rate of 64 pounds/night (without breakfast), until 19 May. To book one of these rooms (for any number of days), contact Staycity at +44 1904 626311, and quote University of York, Mathematics Department, reservation number "Block 786428". You'll need a credit card to hold the booking, but will only need to pay when you check-in. Cancellation is free until 24 hours prior to the date of arrival.

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