code: static Selector convertRange(Selector expr, Selector bound1, Selector bound2) {
      return new OperatorImpl(Operator.AND,
                          new OperatorImpl(Operator.GE, (Selector) expr.clone(), bound1),
                          new OperatorImpl(Operator.LE, (Selector) expr.clone(), bound2));
    }
docs: Convert a partially parsed BETWEEN expression into its more primitive form as a
  conjunction of inequalities.
  
  @param expr the expression whose range is being tested
  
  @param bound1 the lower bound
  
  @param bound2 the upper bound
  
  @return a Selector representing the BETWEEN expression its more primitive form