VanLehn, K. (1987). Learning one subprocedure per lesson. Artificial Intelligence, 31,1-40.

SIERRa is a program that learns procedures incrementally from examples, where an example is a sequence of actions. SIERRA learns by completing explanations. Whenever the current procedure is inadequate for explaining (parsing) the current example, SIERRA formulates a new subprocedure whose instantiation completes the explanation (parse tree). The key to SIERRA'S success lies in supplying a small amount of extra information with the examples. Instead of giving it a set of examples, under which conditions correct learning is provably impossible, it is given a sequence of "lessons," where a lesson is a set of examples that is guaranteed to introduce only one subprocedure. This permits unbiased learning, i.e., learning without a priori, heuristic preferences concerning the outcome.

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