There’s yet another conference in this fast-paced series, and this time it’s in Southern California!

• Symposium on Compositional Structures 4, 22–23 May, 2019, Chapman University, California.

The Symposium on Compositional Structures (SYCO) is an interdisciplinary series of meetings aiming to support the growing community of researchers interested in the phenomenon of compositionality, from both applied and abstract perspectives, and in particular where category theory serves as a unifying common language.

The first SYCO was in September 2018, at the University of Birmingham. The second SYCO was in December 2018, at the University of Strathclyde. The third SYCO was in March 2019, at the University of Oxford. Each meeting attracted about 70 participants.

We welcome submissions from researchers across computer science, mathematics, physics, philosophy, and beyond, with the aim of fostering friendly discussion, disseminating new ideas, and spreading knowledge between fields. Submission is encouraged for both mature research and work in progress, and by both established academics and junior researchers, including students.

Submission is easy, with no format requirements or page restrictions. The meeting does not have proceedings, so work can be submitted even if it has been submitted or published elsewhere. Think creatively—you could submit a recent paper, or notes on work in progress, or even a recent Masters or PhD thesis.

While no list of topics could be exhaustive, SYCO welcomes submissions

with a compositional focus related to any of the following areas, in

particular from the perspective of category theory:

• logical methods in computer science, including classical and quantum programming, type theory, concurrency, natural language processing and machine learning;

• graphical calculi, including string diagrams, Petri nets and reaction networks;

• languages and frameworks, including process algebras, proof nets, type theory and game semantics;

• abstract algebra and pure category theory, including monoidal category theory, higher category theory, operads, polygraphs, and relationships to homotopy theory;

• quantum algebra, including quantum computation and representation theory;

• tools and techniques, including rewriting, formal proofs and proof assistants, and game theory;

• industrial applications, including case studies and real-world problem descriptions.

This new series aims to bring together the communities behind many previous successful events which have taken place over the last decade, including “Categories, Logic and Physics”, “Categories, Logic and Physics (Scotland)”, “Higher-Dimensional Rewriting and Applications”, “String Diagrams in Computation, Logic and Physics”, “Applied Category Theory”, “Simons Workshop on Compositionality”, and the “Peripatetic Seminar in Sheaves and Logic”.

SYCO will be a regular fixture in the academic calendar, running regularly throughout the year, and becoming over time a recognized venue for presentation and discussion of results in an informal and friendly atmosphere. To help create this community, and to avoid the need to make difficult choices between strong submissions, in the event that more good-quality submissions are received than can be accommodated in the timetable, the programme committee may choose to

*defer* some submissions to a future meeting, rather than reject them. This would be done based largely on submission order, giving an incentive for early submission, but would also take into account other requirements, such as ensuring a broad scientific programme. Deferred submissions can be re-submitted to any future SYCO meeting, where they would not need peer review, and where they would be prioritised for inclusion in the programme. This will allow us to ensure that speakers have enough time to present their ideas, without creating an unnecessarily competitive reviewing process. Meetings will be held sufficiently frequently to avoid a backlog of deferred papers.

### Invited speakers

• John Baez, University of California, Riverside: Props in network theory.

• Tobias Fritz, Perimeter Institute for Theoretical Physics: Categorical probability: results and challenges.

• Nina Otter, University of California, Los Angeles: A unified framework for equivalences in social networks.

### Important dates

All times are anywhere-on-earth.

• Submission deadline: Wednesday 24 April 2019

• Author notification: Wednesday 1 May 2019

• Registration deadline: TBA

• Symposium dates: Wednesday 22 and Thursday 23 May 2019

### Submission

Submission is by EasyChair, via the following link:

• https://easychair.org/conferences/?conf=syco4

Submissions should present research results in sufficient detail to allow them to be properly considered by members of the programme committee, who will assess papers with regards to significance, clarity, correctness, and scope. We encourage the submission of work in progress, as well as mature results. There are no proceedings, so work can be submitted even if it has been previously published, or has been submitted for consideration elsewhere. There is no specific formatting requirement, and no page limit, although for long submissions authors should understand that reviewers may not be able to read the entire document in detail.

### Programme Committee

• Miriam Backens, University of Oxford

• Ross Duncan, University of Strathclyde and Cambridge Quantum Computing

• Brendan Fong, Massachusetts Institute of Technology

• Stefano Gogioso, University of Oxford

• Amar Hadzihasanovic, Kyoto University

• Chris Heunen, University of Edinburgh

• Dominic Horsman, University of Grenoble

• Martti Karvonen, University of Edinburgh

• Kohei Kishida, Dalhousie University (chair)

• Andre Kornell, University of California, Davis

• Martha Lewis, University of Amsterdam

• Samuel Mimram, École Polytechnique

• Benjamin Musto, University of Oxford

• Nina Otter, University of California, Los Angeles

• Simona Paoli, University of Leicester

• Dorette Pronk, Dalhousie University

• Mehrnoosh Sadrzadeh, Queen Mary

• Pawel Sobocinski, University of Southampton

• Joshua Tan, University of Oxford

• Sean Tull, University of Oxford

• Dominic Verdon, University of Bristol

• Jamie Vicary, University of Birmingham and University of Oxford

• Maaike Zwart, University of Oxford

The invited speakers will be Tobias Fritz, Nina Otter and me. This will be fun, since Tobias and I wrote a paper together on A Bayesian characterization of relative entropy, and Nina Otter and I wrote one about Operads and phylogenetic trees. They’re both super-smart!