$ ./a.out
Welcome to SWI-Prolog (Multi-threaded, 32 bits, Version 5.10.4)
Copyright (c) 1990-2011 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free 
software, and you are welcome to redistribute it under certain 
conditions. Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- human(socrates).
true.