Rewriting with Frobenius

Abstract

Symmetric monoidal categories have become ubiquitous as a formal environment for the analysis of compound systems in a compositional, resource-sensitive manner using the graphical syntax of string diagrams. Recently, reasoning with string diagrams has been implemented concretely via double-pushout (DPO) hypergraph rewriting. The hypergraph representation has the twin advantages of being convenient for mechanisation and of completely absorbing the structural laws of symmetric monoidal categories, leaving just the domain-specific equations explicit in the rewriting system.In many applications across different disciplines (linguistics, concurrency, quantum computation, control theory,...) the structural component appears to be richer than just the symmetric monoidal structure, as it includes one or more Frobenius algebras. In this work we develop a DPO rewriting formalism which is able to absorb multiple Frobenius structures, thus sensibly simplifying diagrammatic reasoning in the aforementioned applications. As a proof of concept, we use our formalism to describe an algorithm which computes the reduced form of a diagram of the theory of interacting bialgebras using a simple rewrite strategy.