I once launched swi-prolog and asked it a question:
ely:~/home$ prolog Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 5.10.1) Copyright (c) 1990-2010 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). ?- love(math) is unrequited. true.