An intelligent agent acting in a complex and unpredictable world must be able to both plan ahead and react quickly to changes in its surroundings. In particular, such an agent must be able to react quickly when faced with unexpected opportunities to fulfill its goals. W e consider the issue of h o w an agent should respond to perceived opportunities, and w e describe a method for determining quickly whether it is rational to seize an opportunity or whether a more detailed analysis is required. Our system uses a set of heuristics based on reference features to identify situations and objects that characteristically involve problematic patterns of interaction. W e discuss the recognition of reference features, and their use in focusing the system's reasoning onto potentially adverse interactions between its ongoing plans and Uie current opportunity.

Existing planners fall into two broad categories: reactive planners that can react quickly to changes in the world, but do not project the expected results of a proposed sequence of actions, and classical planners that perform detailed projections, but make assumptions that are unrealistic when operating in a complex and dynamic world. Ideally, a planning agent in such a world should be able to do both. In order to do this, the agent has to be able to differentiate between those situations in which detailed information would aid it in making its decisions, and and those in which such information would not materially improve its performance. W e propose an approach to this problem, using well-characterized heuristics to decide what information would be useful, whether to gather it and if so, how.