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One approach to text compression is to replace high-frequency variable-length fragments of words by fixed-length codes pointing to a compression table containing these high-frequency fragments. It is shown that the problem of optimal fragment compression is NP-hard even if the fragments are restricted to prefixes and suffixes. This seems to be a simplest(More)
The most common spelling errors are one extra letter, one missing letter, one wrong letter, or the transposition of two letters. Deletion, exchange, and rotation operators are defined which detect and “mend” such spelling errors and thus permit retrieval despite the errors. These three operators essentially delete a letter of a word, exchange(More)
The problem of automatic digitizing of contour maps is discussed. The structure of a general contour map is analyzed, and its topological properties are utilized in developing a new scanning algorithm. The problem of detection and recognition of contour lines is solved by a two color labeling method. It is shown that for maps containing normal contour lines(More)
A method for compressing large dictionaries is proposed, based on transforming words into lexicographically ordered strings of distinct letters, together with permutation indexes. Algorithms to generate such strings are described. Results of applying the method to the dictionaries of two databases, in Hebrew and English, are presented in detail. The main(More)
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