HOL Light
HOL Light is free software for formally proving mathematical theorems in higher-order logic.
What HOL Light is
HOL Light is free software for formally proving mathematical theorems in higher-order logic. It works as an interactive theorem prover and proof checker with a logical core focused on exact correctness. The system is fully programmable, so users can add theorems and inference rules while preserving soundness. Built-in automated tools and pre-proved theorems cover arithmetic, basic set theory, and real analysis. Written in OCaml, HOL Light is usually used through the OCaml read-eval-print loop, and an official browser version is available. Installation options include OPAM, building from source, and a hol-light package on Debian-based distributions. The documentation covers Linux, macOS, and Windows through WSL or Cygwin, with some native Windows configurations noted. A VS Code extension provides syntax help, terminal interaction, proof-step controls, definitions, goal display, completion, navigation, and notebooks. Tutorials, reference manuals, a HOW-TO, and Zulip chat are provided.
Good
- Free theorem-proving software
- Programmable extensions preserve soundness
- Automated tools and proven theorems
- Browser version available
- VS Code integration documented
Watch out
- Package-manager versions may be outdated
- Requires OCaml-related dependencies
- Windows setup may use WSL or Cygwin
- Self-hosted installation required for local use
Who it suits
HOL Light suits users working with deductive, higher-order-logic theorem proving who are comfortable with OCaml-based tooling. It supports self-hosted installations across Linux, macOS, Windows configurations, and browser use.
Verdict
HOL Light offers a programmable environment for rigorous higher-order-logic proofs, with automation, libraries, browser access, and editor integration. Users should choose installation methods carefully because packaged versions can lag behind source.
The facts
Each one read from HOL Light's own pages, with the date it was checked.
Where it runs
- Applications
- The site cites the Flyspeck project, AWS s2n-bignum, and floating-point verification work at Intel as applications of HOL Light.checked 8 Oct 2026
- Browser access
- The official site links to a browser version that runs HOL Light in a web browser.checked 8 Oct 2026
- Platform notes
- The installation instructions describe Unix-like environments such as Linux and Windows through Cygwin; the README also mentions native Windows support for some configurations.checked 8 Oct 2026
What it does
- Automation and library
- It provides automated tools and pre-proved theorems in areas including arithmetic, basic set theory, and real analysis.checked 8 Oct 2026
- Built-in resources
- It includes automated tools and pre-proved theorems covering areas such as arithmetic, basic set theory, and real analysis.checked 8 Oct 2026
- Dependencies
- The README lists OCaml, camlp5, and either Zarith or Num as dependencies, with the rational arithmetic library depending on the OCaml version.checked 8 Oct 2026
- Documentation
- The official site provides a tutorial and a reference manual in HTML and PDF formats.checked 8 Oct 2026
- Editor integration
- The official site links to a Visual Studio Code extension for HOL Light.checked 8 Oct 2026
- Extensibility
- HOL Light is fully programmable, allowing users to extend it with new theorems and inference rules without compromising soundness.checked 8 Oct 2026
- Extension features
- The linked VS Code extension provides a REPL connection, code completion, hover information, go-to-definition, goal display, and interactive notebooks.checked 8 Oct 2026
- Implementation
- HOL Light is written in OCaml and uses the OCaml toplevel as its front end.checked 8 Oct 2026
- Installation
- The official installation instructions recommend installing HOL Light through OPAM or cloning its GitHub source repository.checked 8 Oct 2026
- Installation limitation
- The tutorial says package-manager versions may be out of date, while building from source provides the latest features.checked 8 Oct 2026
- Language and interface
- HOL Light is written in OCaml and uses the OCaml read-eval-print loop as its usual interaction environment.checked 8 Oct 2026
- Operating systems
- The tutorial discusses Linux, macOS package managers, Windows through WSL or Cygwin, and installation through OPAM across operating systems.checked 8 Oct 2026
- Proof checking
- HOL Light is an interactive theorem prover and proof checker with a logical core the site describes as simple and exacting about correctness.checked 8 Oct 2026
- Purpose
- HOL Light is a computer program for formally proving mathematical theorems in higher-order logic.checked 8 Oct 2026
- Security and trust
- When compiling with HOLLIGHT_USE_MODULE=1, the repository documentation says the trusted base expands to include the inline_loads.ml script.checked 8 Oct 2026
- Support and community
- The official site links to HOL Light Zulip Chat and a written HOW-TO guide.checked 8 Oct 2026
- Support and documentation
- The official site links to a tutorial, reference manual, HOW-TO, and HOL Light Zulip chat.checked 8 Oct 2026
