This is a Prolog style inference system (i.e. a horn clause logic prover) written in Common Lisp. If you are familiar with Prolog, it should be simple to use - you just have to learn a new lisp-flavoured syntax. The top of the code contains documentation on how to use it.
This code is provided free of charge, and without any restrictions on it's use.
Disclaimer: You use this code at your own risk. No warranty is
provided, explicit or implied, as to its fitness for any
purpose. Whilst I have tested it as best I can, it may still contain
bugs or have unwanted side-effects.