- eg: A production system program for sorting a string composed of letters a, b and c -A production is enabled if its condition matches part of string in working memory. -When a rule is fired, the substring that matched the rule condition is replaced by the string on the right-hand side of the rule. -Productions are invoked by the 'pattern' of a particular problem instances Below is an example of production systems used to sort a string in ascending order. You are required to change the rules in the production set so that the system can sort the string in descending order then, do the sorting process until the string is sorted