A randomized algorithm is one which is able to take one or more steps in a non-deterministic fashion, on purpose. Such algorithms are used in many cases. The correctness, or the worst-case or average performance of many deterministic algorithms is often derived from an "adversary argument" which posits the existence of a hypothetical "adversary" who is able to arrange things so as to make things as difficult as possible for the algorithm. In this context, it is often assumed that the adversary has full knowledge of the expected behavior of the algorithm. A randomized algorithm which may behave in several ways at one or more steps may be thought of as a probability distribution on a set of deterministic algorithms (one for each possible choice the randomized algorithm may make). An adversary in such a situation may not be able to devise a single input strategy...