The kernel of ProB is written in Prolog and you can download the latest Prolog sourcecode snapshot from: http://www3.hhu.de/stups/downloads/prob/source/
You may also wish to obtain related Java sources:
The kernel of ProB is written in Prolog and you can download the latest Prolog sourcecode snapshot from: https://stups.hhu-hosting.de/downloads/prob/source/
You may also wish to obtain related Java sources:
The documentation for the Java API to ProB can be found here.
A new ProB Developer Manual is available.