YProlog is a successor of XProlog which is a successor of WProlog.  YProlog is
basically XProlog with easier Prolog-Java interfacing.  Also various minor
changes were made.  The YProlog class provides the Java-Prolog interface (see
javadocs).  

To start YProlog as a command interpreter, use:

    java -jar YProlog.jar

To run the API test example, use:

    java -classpath YProlog.jar yprolog.YProlog

If you compiled the classes, you can also use:

    java yprolog.Go

and

    java yprolog.YProlog

To compile the classes and regenerate the jar:

    javac yprolog/*.java
    javac yprolog/examples/*.java
    jar cmf yprolog/manifest YProlog.jar yprolog/*.class

To recompile the Prolog.jj (compiler-compiler) file, use:

    javacc -output_directory:yprolog yprolog/Prolog.jj

You then need to recompile the classes and jar as necessary.

To recompile the docs:

    javadoc -public -d yprolog/javadocs/ \
        yprolog/YProlog.java yprolog/PrologObject.java


More info:

USERMANUAL          - the user manual describing the YProlog language
javadocs/index.html - the java-prolog interfacing API
LICENSE             - Software license - the revised BSD license.
CHANGES             - History and changelog

YProlog Author info
===================
Boris van Schooten
University of Twente
schooten@cs.utwente.nl
wwwhome.cs.utwente.nl/~schooten/yprolog/

XProlog Author info
===================
Author: Jean Vaucher  
Email:  vaucher@iro.umontreal.ca
URL:    www.iro.umontreal.ca/~vaucher/XProlog/

WProlog Author info
===================
Michael Winikoff 
winikoff@cs.rmit.edu.au
URL: http://goanna.cs.rmit.edu.au/~winikoff/wp/