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A Straight-Line Program (SLP) G for a string T is a context-free grammar (CFG) that derives T only, which can be considered as a compressed representation of T. In this paper, we show how to encode G in n N + (n + n') (n+) + 4n - 2n' + o (n) bits to support random access queries of extracting Tp. . q in worst-case O (N + p - q) time, where N is the length of T, is the alphabet size, n is the number of variables in G and n' n is the number of symmetric centroid paths in the DAG representation for G.
Takasaka et al. (Fri,) studied this question.