title: How to remove duplicate lists in a list of list?
body: <p>I want to remove all duplicates list from a list of list.</p>
  <p>So I have a list of lists like this.</p>
  <pre><code>a = [[1,2],[1,2],[3,4,5],[3,4,5],[3,4,5]]
  </code></pre>
  <p>I want to have:</p>
  <pre><code>b = [[1,2],[3,4,5]]
  </code></pre>
  <p>I don't know how to do it.</p>