title: find trigram using NLTK
body: <p>I am not very familiar with <a href="http://nltk.org/" rel="nofollow">NLTk</a> and python, and I have to do the following tasks in a program:</p>
  
  <ol>
  <li><strong>Tokenize</strong> and lowercase the input <em>text1</em></li>
  <li><strong>Tokenize</strong> the input <em>text2</em></li>
  <li>Find all <strong>trigrams</strong> in the input <em>text1</em></li>
  </ol>
  
  <p>Can anyone help me? </p>