This paper shows how to use Lee, Jones and Ben Amram's size-change principle to check correctness of arbitrary recursive definitions in an ML / Haskell like programming language with inductive and coinductive types. Naively using the size-change principle to check productivity and termination is straightforward but unsound when inductive and coinductive types are nested. We can however adapt the size-change principle to check ``totality'', which corresponds exactly to correctness with respect to the corresponding (co)inductive type.

@article{paperbot3378,
  title = {The Size-Change Principle for Mixed Inductive and Coinductive types},
  author = {Pierre Hyvernat},
  journal = {Logical Methods in Computer Science},
  volume = {Volume 21, Issue 3},
  year = {2025},
  doi = {10.46298/lmcs-21(3:20)2025}
}