The query language as a nondeterministic program

Redesign the query language as a nondeterministic program to be implemented using the evaluator of section 4.3, rather than as a stream process. In this approach, each query will produce a single answer (rather than the stream of all answers) and the user can type try-again to see more answers. You should find that much of the mechanism we built in this section is subsumed by nondeterministic search and backtracking. You will probably also find, however, that your new query language has subtle differences in behavior from the one implemented here. Can you find examples that illustrate this difference?

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