The Zendo rules forbid external references, other than to the surface on which the pieces rest: BNs can't refer to, e.g., "a flat pyramid pointing North," or "the pyramid nearest the Master," or even "the pyramid nearest the edge of the table." Last night, a player wanted to know if the BN could be something like "the shadow of a large pyramid falls upon a small pyramid." I said no, on the grounds that it was a forbidden external reference, but then somebody asked what was external about it, and I had a hard time saying. Was I right anyway? Brian