code: static Selector convertSet(Selector expr, List set) {
      Selector ans = null;
      for (int i = 0; i < set.size(); i++) {
        Selector comparand = (Selector) set.get(i);
        Selector comparison = new OperatorImpl(Operator.EQ, (Selector) expr.clone(), comparand);
        if (ans == null)
          ans = comparison;
        else
          ans = new OperatorImpl(Operator.OR, ans, comparison);
      }
      return ans;
    }
docs: Convert a partially parsed set expression into its more primitive form as a
  disjunction of equalities.
  
  @param expr the expression whose set membership is being tested
  
  @param set the set itself, as a FastVector containing Selector trees representing
  expressions
  
  @return a Selector representing the set expression its more primitive form