DELORES (DEfeasible LOgic REasoning System) is a forward-chaining reasoning engine for defeasible logic, a less expressive but more efficient nonmonotonic logic. In contrast with most other nonmonotonic logics, defeasible logic has linear complexity, allowing DELORES to execute large theories very quickly. DELORES's algorithm extends to general defeasible theories through the use of a preprocessing transformation which eliminates all uses of defeaters and superiority relations. The transformation was designed to provide incremental transformation of defeasible theories, and systematically uses new atoms and new defeasible rules to simulate the eliminated features.

DELORES is Free Software. It is distributed under the terms of the GNU General Public Licence.


The latest version of DELORES is 0.91, released on 2003-12-18. A list of changes from previous versions can be found in the change log.

You can download source packages for the current and previous releases on GitHub or You can also browse, download, or clone the development version on GitHub.

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The distribution includes a Unix man page plus a Programmer's Guide (in LaTeX, DVI, and PDF formats). You can also read the online HTML documentation.

For more information on DELORES and defeasible logic, please visit Michael Maher's publications page.


DELORES was originally conceived by Michael Maher and implemented by Tristan Miller. Development of DELORES was supported by the Australian Research Council under grant A49803544.

Please report bugs to the GitHub issue tracker or by e-mail to Tristan Miller.