Compound u is an aldotertrose that can be oxidized to an optically active aldaric acid, compound v. Upon Wohl degradation, compound u is converted into D-glyceraldehyde. Upon Kiliani-Fisher chain extension, compound U is converted into compounds W and X. Compound W can be oxidized to an optically in active aldaric acid, compound y, but compound x is oxidized to an optically active aldaric acid Z. What are the structures of U through Z?