title: "A is not B" vs "A is (not B)"
body: <p>I'm a little bit scared about the "is not" operator and the possibility that "is not X" is interpreted when "is (not X)" was intended. Do exist some expressions A and B such that:</p>
  
  <pre><code>A is not B
  </code></pre>
  
  <p>is different from</p>
  
  <pre><code>A is (not B)
  </code></pre>
  
  <p>?</p>
  
  <p><strong>addendum</strong>.
  Is it considered good practice to use this operator? Should't <code>not (A is B)</code> be preferred?</p>