《左传·襄公·襄公二十六年》
子产辞去城邑，说： 从上而下，礼数以二的数目递降，这是规定。
子产辞邑，曰： 自上以下，降杀以两，礼也。
Zichan resigned from his position as commander of the capital city, saying: "From top to bottom, rank is diminished by a factor of two - such is the established rule.