A production system consists of a collection of productions (rules), a working memory of facts and an algorithm, known as forward chaining, for producing new facts from old. A rule becomes eligible to "fire" when its conditions match some set of elements currently in working memory. A conflICt resolution strategy determines whICh of several eligible rules (the conflICt set) fires next. A condition is a list of symbols whICh represent constants, whICh must be matched exactly variables whICh bind to the thing they match and "<> symbol" whICh matches a field not equal to symbol. Example production systems are OPS5, CLIPS, flex. (2005-06-17)