Dependently Sorted Theorem Proving for Mathematical Foundations

Authors Yiming Xu , Michael Norrish

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Author Details

Yiming Xu
  • Australian National University, Canberra, Australia
Michael Norrish
  • Australian National University, Canberra, Australia


We appreciate all the anonymous reviewers for their time and effort in pointing out typos and suggesting improvements to this paper. We would also like to thank James Borger for the name "DiaToM", which we feel beautifully encapsulates the aims and nature of our project.

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Yiming Xu and Michael Norrish. Dependently Sorted Theorem Proving for Mathematical Foundations. In 14th International Conference on Interactive Theorem Proving (ITP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 268, pp. 33:1-33:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


We describe a new meta-logical system for mechanising foundations of mathematics. Using dependent sorts and first order logic, our system (implemented as an LCF-style theorem-prover) improves on the state-of-the-art by providing efficient type-checking, convenient automatic rewriting and interactive proof support. We assess our implementation by axiomatising Lawvere’s Elementary Theory of the Category of Sets (ETCS) [F. William Lawvere, 1964], and Shulman’s Sets, Elements and Relations (SEAR) [Michael Shulman, 2022]. We then demonstrate our system’s ability to perform some basic mathematical constructions such as quotienting, induction and coinduction by constructing integers, lists and colists. We also compare with some existing work on modal model theory done in HOL4 [Yiming Xu and Michael Norrish, 2020]. Using the analogue of type-quantification, we are able to prove a theorem that this earlier work could not. Finally, we show that SEAR can construct sets that are larger than any finite iteration of the power set operation. This shows that SEAR, unlike HOL, can construct sets beyond V_{ω+ω}.

Subject Classification

ACM Subject Classification
  • Theory of computation → Logic and verification
  • first order logic
  • sorts
  • structural set theory
  • mechanised mathematics
  • foundation of mathematics
  • category theory


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