[rules-users] How do I write a rule to detect a missing value in a group of facts?

I need to write a rule to identify a missing element in a group of facts. For example, let us say I want to ensure that my fence has a fence post every 8 feet. My fact declaration is as follows: declare FencePost identifier : String distanceFromStart: Long end If I add the following facts into my session: FencePost("a", 0) FencePost("x", 8) FencePost("e", 24) I want a rule that will notify the user that there is a missing fence post between "x" and "e". I've been looking into using "collect" into a TreeSet/TreeMap to get a collection sorted on the "distanceFromStart", but I cannot figure out how to compare adjacent elements in the collection. Any ideas? -- View this message in context: http://drools.46999.n3.nabble.com/How-do-I-write-a-rule-to-detect-a-missi... Sent from the Drools: User forum mailing list archive at Nabble.com.