Allegories of Symbolic Manipulations

Moving from the mathematical theory of (abstract) syntax, we develop a general relational theory of symbolic manipulation parametric with respect to, and accounting for, general notions of syntax. We model syntax relying on categorical notions, such as free algebras and monads, and show that a general theory of symbolic manipulation in the style of rewriting systems can be obtained by extending such notions to an allegorical setting. This way, we obtain an augmented calculus of relations accounting for syntax-based rewriting. We witness the effectiveness of the relational approach by generalising and unifying milestones results in rewriting, such as the parallel moves and the Tait-Martin-Löf techniques.