Just a thought about the Litany of Tarski - be very careful to recognize that the "not" is a logical negation. If the box contains not-a-diamond your assumption will likely be that it's empty. The frog that jumps out when you open it will surprise you!

The mind falls easily into oppositional pairs of X and opposite-of-X (which isn't the same as the more comprehensive not-X), and once you create categorizations, you'll have a tendency to under-consider outcomes that don't categorize.