Please note that the content of this book primarily consists of articles
available from Wikipedia or other free sources online. Bigrams or
digrams are groups of two written letters, two syllables, or two words,
and are very commonly used as the basis for simple statistical analysis
of text. They are used in one of the most successful language models for
speech recognition. They are a special case of N-gram. Gappy bigrams or
skipping bigrams are word pairs which allow gaps (perhaps avoiding
connecting words, or allowing some simulation of dependencies, as in a
dependency grammar). Head word bigrams are gappy bigrams with an
explicit dependency relationship. The term is also used in cryptography,
where bigram frequency attacks have sometimes been used to attempt to
solve cryptograms. See frequency analysis.
