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Over two distinct datasets , we find that indexing according to simple character bigrams produces a retrieval accuracy superior to any of the tested word N-gram models .
 used for: character bigrams, indexing; compare: character bigrams, word N-gram models; evaluate for: retrieval accuracy, character bigrams; evaluate for: retrieval accuracy, word N-gram models
Given options, please tell me the relationships of all the listed entity pairs.Output format is "relation1: word1, word2; relation2: word3, word4". 
Option: conjunction, feature of, hyponym of, used for, part of, compare, evaluate for 
Text: {0} 
 Entity Pairs:  character bigrams, indexing; character bigrams, word N-gram models; retrieval accuracy, character bigrams; retrieval accuracy, word N-gram models 
Answer:
 used for: character bigrams, indexing; compare: character bigrams, word N-gram models; evaluate for: retrieval accuracy, character bigrams; evaluate for: retrieval accuracy, word N-gram models