7. The non-transitory, computer-readable storage medium of claim 1 wherein, when executed, the code causes the processor to determine synonyms by: computing a correlation between the histograms; determining a set S 1 of n-grams whose correlations exceed a threshold; thresholding the set S 1 based on frequency of occurrence of n-grams in the same message to generate a set S 2 of threshoided n-grams; computing distance measures between the n-grams; computing similarity measures as weighted sums of the correlations and the distance measures; thresholding the set S 2 based on the similarity measures to produce a set S 3 ; and the code, when executed, further causes the processor to compute a difficulty metric of each n-gram in set S 3 and select a synonym from the set S 3 based on the difficulty metrics.
1. A non-transitory, computer-readable storage medium containing code that, when executed by a processor, causes the processor to: obtain a plurality of n-grams from a plurality of messages; determine a temporal histogram for each n-gram; determine synonyms among the n-grams based on a correlation of he histograms and a distance measure between n-grams; and select from among the synonyms an n-gram for presentation, wherein the selection is based of a difficulty metric.