title: clojure filter nested map to return keys based on inner map values
body: <p>For this nested map called "tables",</p>
  
  <pre><code>  (def tables 
     {:tableA {:occupied false :party nil} 
      :tableB {:occupied true :party nil}
      :tableC {:occupied false :party nil}})
  </code></pre>
  
  <p>how do I filter and get back the keys where :occupied = false ?</p>
  
  <p>correct result should be <code>(:tableA :tableC)</code></p>
  
  <p>can I do this with "filter" HOF? Should I be using a list comprehension? </p>