A collection of collections. Each instance of agent type by interest is a collection of IntelligentAgents who share an interest in some thing. These will usually be functionally denoted. For example, an agent who likes to collect postage stamps might be a member of (Hobby Interest Fn PostageStamps). Alternatively, she might be a member of (ProductInterestFn PostageStamps) if she wants to use PostageStamps to send mail. Use Has Interest to relate an instance of intelligent agent and the instance of agent type by interest to which the agent belongs.