private static boolean hasSingleOccurrenceInPremise(FormulaVariable variable) {
   if (logger.isTraceEnabled())
     logger.trace("Occurrences for variable: " + variable.toLongString());
   int relationalPremiseOccurrences = variable.getPremiseRelationalOccurrences().size();
   int nonRelationalOccurrences = variable.getNonRelationalOccurrences().size();
   return relationalPremiseOccurrences + nonRelationalOccurrences <= 1;
 }