Fundamentals of Compositional Rewriting Theory

A foundational theory of compositional categorical rewriting theory is presented, based on a collection of fibration-like properties that collectively induce and structure intrinsically the large collection of lemmata used in the proofs of theorems such as concurrency and associativity. The resulting highly generic proofs of these theorems are given; it is noteworthy that the proof of the concurrency theorem takes only a few lines and, while that of associativity remains somewhat longer, it would be unreadably long if written directly in terms of the basic lemmata. In addition to improving, or even enabling, the readability of human-written proofs, we anticipate that this more generic and modular style of writing proofs should organize and inform the production of formalized proofs in a proof assistant such as Coq or Isabelle. A curated list of known instances of our framework is used to conclude the paper with a detailed discussion of the conditions under which the Double Pushout and Sesqui-Pushout semantics of graph transformation are compositional.