# HOL Zero

## What is HOL Zero?

HOL Zero is a basic theorem prover for the HOL logic, designed with
trustworthiness as its top priority. It is primarily intended for two roles:

- A highly-trustworthy system for checking and/or consolidating proofs created on other theorem provers;
- A pedagogical example of a simple theorem prover and its implementation.

Note that some proof porting mechanism is required for the role of checking/consolidating proofs. One such mechanism is under development at Proof Technologies.

Unlike other HOL systems, HOL Zero is NOT primarily targetted at developing proofs, although it is suitable for simple natural deduction proofs. It concentrates on doing basic functionality well, and has relatively sophisticated term parsing, pretty printing and error reporting. Its source code is very carefully written and commented, and aims to be as simple and readable as possible. An extensive glossary of HOL-related
terminology is provided as part of the user documentation.

## Download

A source tarball for the latest version can be downloaded here:
holzero-0.6.2.tgz (released 2013-10-15).

The following are required to run HOL Zero:

- A Unix-like operating system and the bash shell;
- The OCaml
programming language (version >= 3.08);
- The Camlp5
extension to OCaml.

To get started using HOL Zero, unpack the downloaded tarball by entering `tar -xzf holzero-0.6.2.tgz`

at a terminal window, then change to the resulting `holzero-0.6.2`

directory and follow the instructions in Sections 3 and 4 of the README file.

## Unsoundness Bounty

There is a $100 bounty reward for finding soundness-related flaws in HOL
Zero. See here for a list of unsoundnesses and successful claims.

## Contact Us

Email
holzero@proof-technologies.com with any queries, comments or bounty claims,
or simply to tell us you exist. Please help us by mentioning the operating
system(s) you are using with HOL Zero.

To receive occasional news about HOL Zero, email
holnews@proof-technologies.com with "subscribe" in the subject field.