title: Why Cohen-Sutherland algorithm is not appliable on concave polygon?
body: <p>My teacher said that Cohen Sutherland algorithm <a href="http://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm" rel="nofollow">http://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm</a> cannot be used with concave polygon. I asked him why and he could not give me an answer(I don't why hew works here).</p>
  
  <p><strong>So I ask You: Why Cohen-Sutherland algorithm is not appliable on concave polygon? What will go wrong?</strong></p>