Published: 14th December 2023
DOI: 10.4204/EPTCS.397
ISSN: 2075-2180


Proceedings of the Sixth International Conference on
Applied Category Theory 2023
University of Maryland, 31 July - 4 August 2023

Edited by: Sam Staton and Christina Vasilakopoulou

Bicategories of Automata, Automata in Bicategories
Guido Boccali, Andrea Laretto, Fosco Loregian and Stefano Luneia
Subsumptions of Algebraic Rewrite Rules
Thierry Boy de la Tour
Collages of String Diagrams
Dylan Braithwaite and Mario Román
The Algebraic Weak Factorisation System for Delta Lenses
Bryce Clarke
Normalizing Resistor Networks
Robin Cockett, Amolak Ratan Kalra and Priyaa Varshinee Srinivasan
Monoidal Structures on Generalized Polynomial Categories
Joseph Dorta, Samantha Jarvis and Nelson Niu
Syntax Monads for the Working Formal Metatheorist
Lawrence Dunn, Val Tannen and Steve Zdancewic
A Categorical Model for Classical and Quantum Block Designs
Paulina L. A. Goedicke and Jamie Vicary
Constructor Theory as Process Theory
Stefano Gogioso, Vincent Wang-Maścianica, Muhammad Hamza Waseem, Carlo Maria Scandolo and Bob Coecke
Optics for Premonoidal Categories
James Hefford and Mario Román
Overdrawing Urns using Categories of Signed Probabilities
Bart Jacobs and Dario Stein
Effectful Semantics in 2-Dimensional Categories: Premonoidal and Freyd Bicategories
Hugo Paquet and Philip Saville
Structured and Decorated Cospans from the Viewpoint of Double Category Theory
Evan Patterson
Obstructions to Compositionality
Caterina Puca, Amar Hadzihasanovic, Fabrizio Genovese and Bob Coecke
Posetal Diagrams for Logically-Structured Semistrict Higher Categories
Chiara Sarti and Jamie Vicary
String Diagrams with Factorized Densities
Eli Sennesh and Jan-Willem van de Meent
Approximate Inference via Fibrations of Statistical Games
Toby St Clere Smithe
Unifilar Machines and the Adjoint Structure of Bayesian Filtering
Nathaniel Virgo


The Sixth International Conference on Applied Category Theory took place at the University of Maryland on 31 July - 4 August 2023, following the previous meetings at Leiden (2018), Oxford (2019), MIT (2020, fully online), Cambridge (2021) and Strathclyde (2022). It was preceded by the Adjoint School 2023 (24 - 28 July), a collaborative research event in which junior researchers worked under the mentorship of experts. The conference comprised 59 contributed talks, a poster session, an industry showcase session, four tutorial sessions and a session where junior researchers who had attended the Adjoint School presented the results of their research at the school. Information regarding the conference may be found at

ACT 2023 was a hybrid event, with physical attendees present in Maryland and other participants taking part online. All talks were streamed to Zoom and with synchronous discussion on Zulip.

Submission to ACT2023 had three tracks: extended abstracts, software demonstrations, and proceedings. The extended abstract and software demonstration submissions had a page limit of 2 pages, and the proceedings track had a page limit of 12 pages. Only papers submitted to the proceedings track were considered for publication in this volume. In total, there were 81 submissions, of which 59 were accepted for presentation and 18 for publication in this volume. Publication of accepted submissions in the proceedings was determined by personal choice of the authors and not based on quality. Each submission received a review from three different members of the programming committee, and papers were selected based on discussion and consensus by these reviewers.

The contributions to ACT2023 ranged from pure to applied and included contributions in a wide range of disciplines in science and engineering. ACT2023 included talks in linguistics, functional programming, classical mechanics, quantum physics, probability theory, electrical engineering, epidemiology, thermodynamics, engineering, and logic. Many of the submissions had software demonstrating their work or represented work done in collaboration with industry or a scientific organization. The industry session included 9 invited talks by practitioners using category theory in private enterprise.

ACT2023 included four tutorials: David Jaz Myers on Lenses, Paolo Perrone on Markov categories, Dorette Pronk on Double categories, and Evan Patterson and Owen Lynch on AlgebraicJulia.

We are grateful to Angeline Aguinaldo, James Fairbanks, Joe Moeller, and Priyaa Varshinee Srinivasan who played various roles in the ACT organization.

ACT2023 was sponsored by AARMS (Atlantic Association for Research in the Mathematical Sciences), Conexus, DeepMind, NIST (National Institute of Standards and Technology), PIMS (Pacific Institute for the Mathematical Sciences), Quantinuum, University of Florida and 20 Squares.

Sam Staton and Christina Vasilakopoulou
Chairs of the ACT 2023 Programme Committee