You can interrupt the execution of a Prolog program at any time by typing ^c (^c^c under GNU Emacs). For example, if you submit a query to Prolog and then decide you want to stop (abort) the query, type ^c to which Prolog will respond by displaying the message
Prolog interruption (h for help)?
At this point, you can either type h to see a list of the options available to you, as shown below, or you can simply type the letter that corresponds to the option you want to select.
If you type h, Prolog displays the following list of options:
Prolog interrupt options:
h help - this list
c continue - do nothing
d debug - debugger will start leaping
t trace - debugger will start creeping
a abort - abort to the current break level
q really abort - abort to the top level
e exit - exit from Prolog
Prolog interruption (h for help)?
To select an option, type the letter that corresponds to that option and press <RET>. For example, to stop the execution of the current query, type a followed by <RET>. Prolog will print
! Execution aborted
and then return to its top level, displaying the main Prolog prompt.
Typing c causes the current procedure to continue executing as if
nothing had happened. Typing t turns on the trace option of the
debugger (see dbg-bas-con-tdz). Typing d turns on the
debug option of the debugger (see dbg-bas-bas).
Typing a causes the current query to be aborted and the main Prolog
prompt to be redisplayed, as shown above. Typing e ends your Prolog
session.