Command: invis <arg>

Turn yourself invisible.  Arg determines how invisible you are.  Possible
numbers are:

10 - No short description, i.e. you don't appear in the room, and can't
     be seen when you walk around.
20 - No who, i.e. you don't show up on the who list.
30 - Someone, i.e. in most things you will show up as "someone."
40 - Teleportation messages aren't displayed.
50 - Your actions do not show up.
60 - No ID, you will not be accessible by your name at all.
100- You no longer show up on the people list.

(Note that wizards of high levels may be able to override your invisibility.)