  As real logic programmers normally use cut (!), an effective learning
procedure for logic programs should be able to deal with it. Because the cut
predicate has only a procedural meaning, clauses containing cut cannot be
learned using an extensional evaluation method, as is done in most learning
systems. On the other hand, searching a space of possible programs (instead of
a space of independent clauses) is unfeasible. An alternative solution is to
generate first a candidate base program which covers the positive examples, and
then make it consistent by inserting cut where appropriate. The problem of
learning programs with cut has not been investigated before and this seems to
be a natural and reasonable approach. We generalize this scheme and investigate
the difficulties that arise. Some of the major shortcomings are actually
caused, in general, by the need for intensional evaluation. As a conclusion,
the analysis of this paper suggests, on precise and technical grounds, that
learning cut is difficult, and current induction techniques should probably be
restricted to purely declarative logic languages.
