Finding differences between two Prolog files

This simple program works like the good old diff but for files that contain Prolog code. It prints out the clauses that it finds are different in the files. Its use avoids textual differences such as different variable names and different formatting of the code in the files.

    pldiff <file1> <file2>
       : find differences 

    pldiff -h
       : print this information

   pldiff( <filename> , <filename> )