Don’t go hunting in the attic for your 5-1/4-inch Turbo Prolog floppy, though. Although Jess, a Java-based engine developed at Sandia Labs, has roots in both Lisp and Prolog, the emerging ...

Prolog uses the rules to satisfy a query (using modus ponens, if-then, basically). A common approach they may (I'm not going to research it ) have used is iterative deepening to avoid this problem.