title: Scheme: function, returning the list of numbers
body: <p>Write a function <code>(pick-numbers-simple L)</code>. </p>
  
  <p><code>L</code> is a simple list, which does not contain nested lists.</p>
  
  <p>The result of the function is a list of the numbers in <code>L</code>.</p>
  
  <p>The appearance order of the numbers in the result list should be the same as that in <code>L</code>. For example, the result of <code>(pick-numbers-simple (list a b 1 2 c 3 d))</code> should be <code>(1 2 3)</code>.</p>
  
  <p>I have a whole lot of them to write, i just need a head start. If I can get a help on this one, I can do the rest.</p>