title: Example of arc consistency does not imply satisfiability
body: <p>I've read that arc consistency does not imply satisfiability.
  The provided example was</p>
  
  <pre><code>X in D ∧ Y in D ∧ X ≠ Y ∧ X = Y
  </code></pre>
  
  <p>for domains D with more than one value.</p>
  
  <p>My understanding is that for each of the possible values of X (from D) there are values of Y (from the same D) such that the above constraint is satisfied.</p>
  
  <p>Could someone please give me an example of this?</p>