[YeGoblynQueenne]

>> getting Prolog to do cool things quickly involved knowing precisely where to put cut operators, and that was basically black magic. But it's been a while.

To add to tom_mellior's much upvoatable reply, I find that the cut is much less painful if you keep your predicates small and mind separation of concerns, as you should anyway.

A good recommendation about when to use the cut operator is "as soon as undesired nondeterminism happens". With short and to-the-point predicates this is much easier to do.

Finally- the Prolog community has a term for two types of cut, the "green cut" and "red cut". A green cut is a cut that simply stops non-productive backtracking, which checks subsequent clauses and fails. A red cut is one that has the potential to significantly change the behaviour of the program by stopping subsequent clauses from being executed even when they could be true.

[1] Frex, see this very nice resource: "Coding Guidelines for Prolog", Covington, Bagnara, O'Keefe, Wielemaker and Price. Online here: https://arxiv.org/pdf/0911.2899.pdf