title: Arango AQL queries NOT IN
body: <p>I'm creating a Facebook-like website and I want to suggest friends for a user who studies at the same school, but are not already friends.</p>
  
  <p>I already Trying to do this with AQL queries, but there seems to be a syntax problem..</p>
  
  <p>The error code return was: </p>
  
  <blockquote>
    <p>syntax error, unexpected identifier near 'user._key not in (for friend in ...' at position 3:3 (while parsing)</p>
  </blockquote>
  
  <pre><code>for user in users
    filter user._key != "myself"
      user._key not in (for user in 1..1 outbound "users/myself" friendship return user) 
        user._key not in (for user in 1..1 outbound "users/myself" schoolStudies return user)
      return user
  </code></pre>