I've been doing a lot of thinking about Zendo, and as I'm an out-of-the-box kind of person, I've been trying to think of rule-pairs, where the only difference between the rules is whether or not the Null Koan has the buddha nature. For those not familiar, the Null Koan is the Koan that has exactly zero pyramids in it. Some example rules and how the Null Koan fits are: AKHTBNIAOI there are no red pieces in it (Null, having no pieces at all, has BN) AKHTBNIAOI the number of yellow pieces is the same as the number of green pieces (Null, means zero yellow and zero green, thus equal, thus has BN) AKHTBNIAOI it has at least 4 pips (Null has zero pips, do does not have BN) So, further to that, an example of the rule pairs I'm thinking of: 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'm pretty sure that Null is the only koan that can differentiate these two. Can you think of others? Timothy