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4.5.1 How to Raise the HALT condition
The implementation connect the HALT condition to an external
event, which might be the pressing of certain key combination. The
common conventions of the operating system will dictate what that
combination of keystrokes is.

Below is a list, which describes how to invoke an event that will
raise the HALT condition under various the operating systems which
Regina runs under.

·    Under various variants of the Unix operating system, the HALT
  event it connected to the signal “interrupt” (SIGINT). Often this
  signal is bound to special keystrokes.  Depending on your version
  of Unix, this might be <ctrl>-<c> (mostly BSD-variants) or the
  <del> key (mostly System V).  It is also possible to send this
  signal from the command line, in general using the program
  kill(1); or from program, in general using the call signal(3).
  Refer to your Unix documentation for more information.

·    Under VAX/VMS, the key sequence <ctrl>-<c> is used to raise
  the HALT condition in the interpreter.