Tallinn University of Technology

Nathan Joseph Haydon, the PhD student of the Department of Software Science, will defend his PhD thesis "Peirce’s Existential Graphs and the Logic of String Diagrams" on June 6, 2024, starting at 14:00. The defense will take place in room ICT-638 (Akadeemia tee 15a, ICT building of TalTech) and can be also followed via Zoom.

String diagrams are a viable alternative to more traditional algebraic syntax, often yielding an elegant presentation of the relational features under consideration and one that allows for the treatment of variables and algebraic operations in a compositional manner. Following the pioneering work of Charles S. Peirce, who developed a graphical logic of relations over 100 years ago in his Existential Graphs, we treat here and extend the logical aspects of string diagrams. The key developments follow from a renewed emphasis on Peirce’s scroll — a sign of two nested circles serving at once as an inclusion and an involution — that allows us to capture various logical connectives and other operations. The result is a contemporary graphical relational calculus sufficient to serve as a foundation for large portions of mathematics and for applications to logic and fields like knowledge representation.

The thesis is published in the Digital Collection of TalTech Library.

Supervisor Prof Pawel Maria Sobocinski and co-supervisor Leading Researcher Ahti-Veikko Juhani Pietarinen.


  • Dr. David Corfield, University of Kent, UK;
  • Dr. Todd Hampton Trimble, Western Connecticut State University, USA.

Follow public defence in Zoom

Meeting ID: 998 2555 6692
Passcode: 035727