title: Sum of two nested lists
body: <p>I have two nested lists:</p>
  
  <pre><code>a = [[1, 1, 1], [1, 1, 1]]
  b = [[2, 2, 2], [2, 2, 2]]
  </code></pre>
  
  <p>I want to make:</p>
  
  <pre><code>c = [[3, 3, 3], [3, 3, 3]]
  </code></pre>
  
  <p>I have been referencing the <code>zip</code> documentation, and researching other posts, but don't really understand how they work. Any help would be greatly appreciated!</p>