[rules-users] Check if fact is subset of items in the rule

Posting a new thread for this specific problem that has been a head scratcher for me for days now. Here is the problem space. I have a rule that can have a superset of elements such as say "String1", "String2", "String3" , "String4". These are known in rule creation time. Fact can have subset say "String1", "String4" How can I form a drl to check to verify that fact is a subset of elements in the rule? I need to not fire the rule if fact is a subset but I should be able to add a not if I can first figure out if it is a sub set. Any help would be greatly appreciated. Thanks Kumar