Magic tree

The goal of the OpenTheory project is to allow specifications and proofs to be shared between different theorem prover implementations of higher order logic, including HOL Light, HOL4 and ProofPower. OpenTheory packages are a common format to build a standard library of formalized mathematics and verified software.

Get started with OpenTheory by downloading the opentheory tool.


  • 2017: The hol Haskell library for reading and pretty-printing OpenTheory packages.
  • 2016: First publication of a standard for interpretation files describing symbol renamings.
  • 2014: OpenTheory interfaces have been developed for HOL Light, HOL4 and ProofPower.
  • 2011: Launch of the Gilith OpenTheory repo to support community development of theory packages.
  • 2010: First publication of a standard for theory files describing theory packages.
  • 2009: First release of the open source opentheory tool to process theory packages.
  • 2007: First publication of a standard for article files containing proofs of theorems.
  • 2004: The project was initiated by Joe Leslie-Hurd (HOL4) and Rob Arthan (ProofPower).


Theorem Prover Interfaces

Here are the current theorem prover implementations that can read (R) and/or write (W) theories in OpenTheory format:

Theorem ProverR/WMaintainer
HOL LightR/WJoe Leslie-Hurd
HOL4R/WRamana Kumar
ProofPowerR/WRob Arthan
IsabelleRRamana Kumar and Michael Norrish