Below are a few references on Prolog. Any of the texts should serve as a good reference. Since you've all had some experience with Prolog you probably won't need these. To quickly look up a few things, you might try one of the online references.
The prolog system that we recommend is SWI Prolog. SWI Prolog is invoked by the command "pl" on CDF.
You can also download a version of SWI for your PC (linux, Windows, or Mac).
See the SWI home page for downloads, and documentation.
Some additional material on Prolog.