[rules-users] Drools rule writing question

Hello, I am new to Drools. We have been using JESS for a while and ran into a problem that we cannot solve and is hoping Drools have a solution. Is there anything in the Drools language / rules that allows for temporal evaluation within the rules? What I mean is, say your rule examines 2 variables, var1 and var2, and if both are true it fires. Is there any way/technique to say "If var1 becomes true and var2 was ALREADY true, fire" and "If var1 was ALREADY true and var2 becomes true, DO NOT fire?" I've worked w/ JESS and there is nothing built into the language that does this. Is there something in Drools that can handle this or some general techniques that can deal with something like this? Thanks. Denny