We are happy to announce that BCTCS is coming back to Swansea next year. More details to follow.

# Category Archives: Event

# Our PhD students to present at BCTCS2021

Arved will give a talk on Propagator Networks for Unification and Proof Search on Monday (29.03) and Jay will present his research on Trustable Machine Learning Systems on Tuesday (30.03).

# Talk by Adam Ó Conghaile

Today Adam Ó Conghaile will give a talk on “Games & Comonads in Finite Model Theory” as a part of our Theory Seminar Series.

**Abstract.** Model-comparison games (such as Ehrenfeucht-Fraïssé games, pebble games and modal bisimulation) capture various approximations to isomorphism and homomorphism between structures. These approximations are important and well-studied in computer science for their connections with logic and algorithms but their descriptions are often ad hoc and unified approach to these games is lacking in classical finite model theory. Game comonads, introduced by Abramsky, Dawar & Wang [1], provide a categorical semantics for these games which reveals connections between these games and relates them in a surprising and elegant way to structural parameters such as treewidth.

In my talk, I will survey the landscape of model-comparison games and developments in this new comonadic perspective to them, including contributions from my recent work with Anuj Dawar on game comonads for logics with generalised quantifiers. [2]

[1] – S. Abramsky, A. Dawar, P. Wang *The pebbling comonad in finite model theory*, LiCS 2017

[2] – A. Ó Conghaile, A. Dawar *Game comonads & generalised quantifiers*, CSL 2021

# Celebrating World Logic Day at Swansea

Roger Hindley will give a talk on “100 Years of Combinatory Logic” on Friday, 22 January 2021 as a part of the World Logic Day celebration here in Swansea.

Time: Jan 22, 2021 10:00 AM London

Join Zoom Meeting by following this link.

Meeting ID: 965 2656 4560 Passcode: 411495

UNESCO proclaimed World Logic Day in 2019 in association with the International Council for Philosophy and Human Sciences (CIPSH), to enhance public understanding of logic and its implications for science, technology and innovation.

A complete list of WLD 2021 events can be found at http://www.wld.cipsh.international/wld.html.

# Tonicha is speaking at UW-Madison logic seminar

Our PhD student, Tonicha Crook, is giving a talk at UW-Madison logic seminar today at 3pm.

__Title:__

The Weihrauch Degree of Finding Nash Equilibria in Multiplayer Games

__Abstract:__

Is there an algorithm that takes a game in normal form as input, and outputs a Nash equilibrium? If the payoffs are integers, the answer is yes, and a lot of work has been done in its computational complexity. If the payoffs are permitted to be real numbers, the answer is no, for continuity reasons. It is worthwhile to investigate the precise degree of non-computability (the Weihrauch degree), since knowing the degree entails what other approaches are available (eg, is there a randomized algorithm with positive success change?). The two player case has already been fully classified, but the multiplayer case remains open and is addressed here. As well as some insight into finding the roots of polynomials, which is essential in our research. An in-depth introduction to Weihrauch Reducibility will be included in the presentation, along with a small introduction to Game Theory.

# BCTCS 2020 going ahead

In spite of the COVID-19 outbreak, we are glad to host BCTCS 2020 starting today, even if virtually. For more information on invited and contributed talks, check the official BCTCS 2020 website.

# Seminar series on Computability Theory and its Applications

Our colleague Arno Pauly is on the Programme Committee of the Computability Theory and its Applications seminar series, which currently is taking place virtually.

The seminar now has a YouTube channel where you can find the recordings of past talks you may have missed. The information on future talks, the timings of those, and the links to the videos are all available on the webpage here:

# 2nd World Logic Day

Today as a part of the 2nd World Logic Day our Theory group commemorated the work of Erik Palmgren (1963-2019), who sadly passed away last year.

Anton Setzer presented Erik’s most influential papers, which had a big impact on Anton’s own research.

# Meeting to commemorate the logician Erik Palmgren (1963-2019) on the occasion of the World Logic Day

We meet to remember the great logician Erik Palmgren who sadly passed away in November 2019 .

To honor Erik Palmgren’s work, Anton Setzer will give a talk with the title:

*Palmgren’s interpretation of inductive definitions in type theory and development of higher type universes in type theory.*

The meeting also marks the 2nd World Logic Day.

Venue: Theory Lab (CoFo 209)

Time: 14th of January 2020, 2-3 pm

# 2nd Proof Society Workshop on Proof Theory and its Applications

Following the Summer School, we are really proud to host the 2nd Proof Society Workshop. The workshop was an opportunity to listen to a lot of interesting invited and contributed talks on proof theory and various areas of its application:

**Adam Wyner:** Computational Law – The Case of Autonomous Vehicles

**Yong Cheng:** Exploring the incompleteness phenomenon

**Matthias Baaz:** Towards a Proof Theory for Henkin Quantifiers

**Sonia Marin:** On cut-elimination for non-wellfounded proofs: the case of PDL

**Gilles Dowek:** Logical frameworks, reverse mathematics, and formal proofs translation

**Benjamin Ralph:** What is a combinatorial proof system?

**William Stirton:** Ordinal assignments correlated with notions of reduction

**Oliver Kullmann:** Practical proof theory: practical versions of Extended Resolution

**Anton Setzer** and** Ulrich Berger **on behalf of **Ralph Matthes:** Martin Hofmann’s case for non-strictly positive data types – reloaded

**Laura Crosilla:** Philosophy of mathematics and proof theory

**Takako Nemoto:** Recursion Theory in Constructive Mathematics

**Arno Pauly:** Combinatorial principles equivalent to weak induction

**Antonina Kolokolova:** The proof complexity of reasoning over richer domains

**Joost Joosten:** The reduction property revisited

**Helmut Schwichtenberg:** Computational content of proofs

Thanks to all the speaker and participants and we hope to see you all again soon.