title: How to sync two planning entities to a value
body: <p>I want to sync planning values between two planning entities. In this case, I want to make two <code>SubjecTeacherPeriod</code> choose periods that "coincide" with each other, even though their possible value ranges are disjoint. </p>
  
  <pre><code>STP s1: period-N/A periodList-&gt;[1,2,3,4,5,6]
  STP s2: period-N/A periodList-&gt;[106,107,108,109,110,111]
  SyncConstraint(leftSTP = s1,rightSTP = s2)
  &lt;A rule for SyncConstraint that checks if s1.period and s2.period are compatible&gt;
  </code></pre>
  
  <p>For example <code>Period</code>s <code>1</code> and <code>106</code> are compatible as they are both "first hours of Monday". Likewise for <code>2</code> and <code>107</code>.</p>
  
  <p>I did set planning entity difficulty which assigns <code>s2</code> right after <code>s1</code> (I saw the log). But they are assigned values which are not compatible. And the system never recovers from such an error at the end of the solver action.</p>
  
  <p>How can I make them sync?</p>
  
  <hr>
  
  <p>Where I mentioned "compatible" and "coincide", I mean <code>Period</code>s which have two fields (day of week and day order) equal. Each class (and each <code>SubjectTeacherPeriod</code> whose possible periods in that class) has separate <code>Period</code>s.</p>