Hybrid bigram part of speech tagger.

The hybrid bigram part of speech tagger assigns tags to words in a sentence using the most probable set of tags as determined by a bigram hidden Markov model, given the possible tags of the previous words. The Viterbi algorithm is used to reduce the amount of computation required to find the optimal tag assignments. A rule-based retagger applies a set of rules to correct the initial tags emitted by the bigram model.