Question: The disjointness problem for an instance (U, V ) can be solved by a deterministic protocol by sending the complete data of one computer to the other. In this way, the communication complexity is n·|U| or n·|V |, but it is never necessary to exchange more than 2n bits. Explain why 2n bits always suffice. Do there exist cardinalities of U and V such that the randomized protocol PDisj is not better than an optimal deterministic protocol?