“…Therefore, it is not surprising that those who contribute first gain less than the defector players who just enjoy the fruit of others' efforts. This annoying conclusion cannot be avoided, just only if we assume some additional circumstance, like punishing defectors, rewarding cooperators [24,25,26,27,28,29], or other more sophisticated mechanism which allows cooperators to collect competitive payoff [30,31,32,33,34,35,36,37,38,39,40].…”