Aborting is implemented by throwing the reserved exception '$aborted'. This exception can be caught using catch/3, but the recovery goal is wrapped with a predicate that prunes the choice points of the recovery goal (i.e., as once/1) and re-throws the exception. This is illustrated in the example below, where we press control-C and `a'. See also section 4.11.1.

?- catch((repeat,fail), E, true).
^CAction (h for help) ? abort
% Execution Aborted