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The use of "cut" is a well known performance enhancement for Prolog-style rules. In KnowledgeWorks it does more than reduce the time spent in search. When a "cut" is invoked, all the stack space between the initial call to the containing rule and the current stack location is reclaimed immediately, and can have a significant impact on the total space requirements of a program.

KnowledgeWorks and Prolog User Guide - 4 Apr 2005