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.