Brill tagging (5.6)

Brill tagging concept is shown in the textbook. This is an example in NLTK.

>>> nltk.tag.brill.demo()
Loading tagged data... 
Done loading.
Training unigram tagger:
    [accuracy: 0.832151]
Training bigram tagger:
    [accuracy: 0.837930]
Training Brill tagger on 1600 sentences...
Finding initial useful rules...
    Found 9757 useful rules.

           B      |
   S   F   r   O  |        Score = Fixed - Broken
   c   i   o   t  |  R     Fixed = num tags changed incorrect -> correct
   o   x   k   h  |  u     Broken = num tags changed correct -> incorrect
   r   e   e   e  |  l     Other = num tags changed incorrect -> incorrect