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.
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. 2. The non-transitory, computer-readable storage medium of claim 1 wherein, when executed, the code causes the processor to compute a similarity measure between n-grams.