Just an example of how to perform boolean operation as I think you are trying to do. This depends on bool being cast to int where true = 1 and false = 0.
Not(Not(X) + Not(Y) + Not(Z) = 1)
This will return a boolean False if and only if one of X, Y, or Z are False
If the automatic casting does not work you might try a logical expression like this:
Not((If X then 0 else 1)+(If Y then 0 else 1)+(If Z then 0 else 1)=1)
Hope this helps