We present a new design for an algebraic simplification library structured around concepts from universal algebra: theories, models, homomorphisms, and universal properties of free algebras and free extensions of algebras. The library’s dependently typed interface guarantees that both built-in and user-defined simplification modules are terminating, sound, and complete with respect to a well-specified class of equations. We have implemented the design in the Idris 2 and Agda dependently typed programming languages and shown that it supports modular extension to new theories, proof extraction and certification, goal extraction via reflection, and interactive development.

@article{paperbot3054,
  title = {Frex: Dependently Typed Algebraic Simplification},
  author = {Guillaume Allais and Edwin Brady and Nathan Corbyn and Ohad Kammar and Jeremy Yallop},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {9},
  number = {ICFP},
  year = {2025},
  doi = {10.1145/3747506}
}