 Basically, the agent’s ranking of elements of her domain of preference must be complete and transitive. Completeness means only that the agent, when presented with any pair A and B of elements in her domain of preference can rank A and B. That is, the agent either prefers A to B, prefers B to A, or is indifferent between A and B. Some, but not all, relations are complete. The relation “Pareto superior to,” discussed at length in section 6.2, for example, is not complete.