# Natural Language Toolkit: code_three_word_phrase

 from nltk.corpus import brown
 def process(sentence):
     for (w1,t1), (w2,t2), (w3,t3) in nltk.trigrams(sentence): # [_three-word]
         if (t1.startswith('V') and t2 == 'TO' and t3.startswith('V')): # [_verb-to-verb]
             print(w1, w2, w3) # [_print-words]

 >>> for tagged_sent in brown.tagged_sents():
 ...     process(tagged_sent)
 ...
 combined to achieve
 continue to place
 serve to protect
 wanted to wait
 allowed to place
 expected to become
 ...