“…For various problems, the RS structure results in solutions which are consistent with the available rigorous bounds [12], [13], [18], [20]. There are, however, several examples in which the RS ansatz does not give valid solutions [6], [14], [21], [22]. For these cases, it is believed that the problem is caused by the assumed structure, i.e., RS, and therefore, more general structures are supposed to result in valid solutions.…”