title: Common elements between two lists with no duplicates
body: <p>Problem is this, take two lists, say for example these two:</p>
  
  <pre><code>a = [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
  b = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
  </code></pre>
  
  <p>And write a program that returns a list that contains only the elements that are common between the lists (without duplicates). Make sure your program works on two lists of different sizes.</p>
  
  <p>Here's my code:</p>
  
  <pre><code>a = [1, 1, 2, 2, 3, 5, 8, 13, 21, 34, 55, 89]
  b = [1, 2, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
  c = []
  for i in a:
      if i in b and i not in c:
          c.append([i])
  print(c)
  </code></pre>
  
  <p>My output is still giving me duplicates despite the 'i not in c' statement. why is this? I'm sure its blatantly obvious, I just cant see it!</p>