How to start the Prolog interpretor

Here is a sample session. user input is shown in bold. The unix promt is shown in red. prep cs130f
[cs130f] -bash-3.1$ pl

Welcome to SWI-Prolog (Multi-threaded, 32 bits, Version 5.6.62)
Copyright (c) 1990-2008 University of Amsterdam.
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit for details.

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

?- halt.
[cs130f] -bash-3.1$ 

[cs130f] -bash-3.1