Well, the trouble with the Null koan, and why it has been ruled illegal in the base rules of Zendo, is that people can interpret it differently. So in your example: > 1a) AKHTBNIAOI it has no red pieces (Null has BN) > 1b) AKHTBNIAOI if only consists of blue or green or yellow pieces or > any combination of those three (Null, as it does not contain at least > one blue or green or yellow, does not have BN) I could say that in 1b) the null koan DOES have the BN since it has no pieces that contradict your rule. It has no pieces that are NOT Yellow, Green, nor Blue. I believe that someone pointed out a while ago that in general, this shows a difference in the way easterners think compared to westerners. Unfortunately I have no time to dig through my archives right now, but perhaps in a couple days I will see what info I can pull together on this topic. - Dan P.S.> By the way, you could make most rules into your two-part style by stating it one way as "must have at least one piece" (== "the null koan does NOT have the BN") and the other way without that condition. (Or force the second version with the condition that "the null koan has BN".)