[rules-users] Action firing twice

Hello All,I have a list of Items that I am inserting into working memory. Here is the rule that is failing:rule "Cannot select X if both Y and Z are not selected"when    Item(code == "X")    (or (not Item(code == "Y"))        (not Item(code == "Z")))then    System.out.println("Error: You cannot select X unless both Y and Z are selected");endThis rule works correctly when X and Y are there, and when X and Z are there. However, when both Y and Z are missing, the error prints twice. Can anyone tell me what I am doing wrong.Thanks a lotVithal