Introducing String Diagrams: The Art of Category Theory

String diagrams are powerful graphical methods for reasoning in elementary category theory. Written in an informal expository style, this book provides a self-contained introduction to these diagrammatic techniques, ideal for graduate students and researchers. Much of the book is devoted to worked examples highlighting how best to use string diagrams to solve realistic problems in elementary category theory. A range of topics are explored from the perspective of string diagrams, including adjunctions, monad and comonads, Kleisli and Eilenberg–Moore categories, and endofunctor algebras and coalgebras. Careful attention is paid throughout to exploit the freedom of the graphical notation to draw diagrams that aid understanding and subsequent calculations. Each chapter contains plentiful exercises of varying levels of difficulty, suitable for self-study or for use by instructors.

Ralf Hinze is Professor of Software Engineering at the University of Kaiserslautern–Landau (RPTU). His research is centered around the construction of provably correct software, with a particular emphasis on functional programming, algebra of programming, applied category theory, and persistent data structures. His goal is to develop theory, languages, and tools that simplify the construction of reliable software systems.

Dan Marsden is a theoretical computer scientist currently working as Transitional Assistant Professor at the University of Nottingham. He is interested in the foundations of computer science, logic, and mathematics, with particular emphasis on the application of category theory.