If i create a trigger expression like: send me a message when "a=0 and b=0", so i expecting that i'm getting a new message, when someone of them is not equal 0 any more. The negation of (a=0 and b=0) is (a!=0 or b!=0) (Propositional calculus- https://en.wikipedia.org/wiki/Propositional_calculus) So i want to know, if someone of them aren't equal zero again.