title: How to get current system year in Prolog as a number
body: <p>How to get current system year as a number in prolog.
  I found this.
  But it gives the year as a string.</p>
  
  <pre><code>today(Today) :- get_time(X), format_time(atom(Today), '%Y', X).
  </code></pre>
  
  <p>Thanks.</p>