Abstract
In this paper, we study the generalization algorithms for second-order terms, which are treated as first-order terms with function variables, under an instantiation order denoted by≽. First, we extend the least generalization algorithm lg for a pair of first-order terms under≽, introduced by Plotkin and Reynolds, to the one for a pair of second-order terms. The extended algorithm lg, however, is insufficient to characterize the generalization for a pair of second-order terms, because it computes neither the least generalization under≽nor the structure-preserving generalization. Since the transformation rule for second-order matching algorithm consists of an imitation and a projection, in this paper, we introduce the imitation-free generalization algorithm ifg and the projection-free generalization algorithm pfg. Then, we show that ifg computes the least generalization under≽of any pair of second-order terms, whereas pfg computes the generalization equivalent to lg under≽. Nevertheless, neither ifg nor pfg preserves the structural information. Hence, we also introduce the algorithm spg and show that it computes a structure-preserving generalization. Finally, we show that the algorithms lg, pfg and spg are associative, while the algorithm ifg is not.
This work is partially supported by Grand-in-Aid for Scientific Research 15700137 and 16016275 from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and 13558036 from the Japan Society for the Promotion of Science.
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Hirata, K., Ogawa, T., Harao, M. (2004). Generalization Algorithms for Second-Order Terms. In: Camacho, R., King, R., Srinivasan, A. (eds) Inductive Logic Programming. ILP 2004. Lecture Notes in Computer Science(), vol 3194. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-30109-7_14
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DOI: https://doi.org/10.1007/978-3-540-30109-7_14
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