Cut (logic programming)

The cut, in Prolog, is a goal, written as !, which always succeeds but cannot be backtracked. Cuts can prevent unwanted backtracking, which could add unwanted solutions and/or space/time overhead to a query.

The cut should be used sparingly. While cuts can be inserted into code containing errors, if a test is unnecessary because a cut has guaranteed that it is true, it is good practice to say so in a comment at the appropriate place.

Some programmers call the cut a controversial control facility because it was added for efficiency reasons only and is not a logical formula.