An example of case retrieval is illustrated in Figure 15.
Assume that a new problem which is to be attempted through replay contains three goals, (AT-OB OB1 ld), (AT-OB OB2 ld), and (AT-OB OB3 ld). The second goal negatively interacts with both of the other goals. The retriever will first attempt to find a case that solves the first goal alone. Case A solves this goal. However, this case is annotated with a failure reason which is satisfied in the new problem situation, and A is therefore censored in favor of the repairing case, Case B. Once the retriever returns Case B, it will then have one open goal not covered, that is, (AT-OB OB3 ld). It will seek out a case which solves this goal alone, and will again find Case A. However, A's failure reason is again satisfied in the new problem state and will be rejected in favor of a second copy of B (which we now call Case B'), which solves the problem of transporting both OB3 and OB2. There will then be two instances of Case B that will be retrieved to solve the three goal problem, Case B and Case B'. Together they cover the new problem goals. DERSNLP+EBL replays both copies of B in sequence to obtain a solution to the full problem, thereby merging their respective subplans. Notice, however, that the union of these plans will contain redundant steps. For example, both plans have the plane fly to location l1. Section 3.3 describes how DERSNLP+EBL deals with these positive goal interactions.