U-ness

But I do not think that this marks any contrast between the concepts of redness and U-ness. Even with the biconditional linking U-ness with Sloanes, it is possible to offer a contingent reading that expands the possibilities of error. It is possible to understand the biconditional so that what matters for U-ness at any world is what the Sloane Square set says in the actual world, not what it says at the world in question.