METRIC METHODS 3 EXAMPLES AND A THEOREM

The existence of a model for a logic program is generally established by lattice-theoretic arguments. We present three examples to show that metric methods can often be used instead, generally in a direct, stra ightforward way. One example is a game program, which is not stratifie d or locally stratified, but which has a unique supported model whose existence is easily established using metric methods. The second examp le is a program without a unique supported model, but having a part th at is ''well-behaved.'' The third example is a program in which one pa rt depends on another, illustrating how modularity might be treated me trically. Finally we use ideas from this third example to prove a gene ral result from Apt and Padreschi. The intention in presenting these e xamples and the theorem is to stimulate interest in metric techniques, and is not to present a fully developed theory.