《史记·三十世家·赵世家》
左师公说： 从现在上推到三代以前，直到赵国每位君主的子孙被封侯的，他们的继承人还有在位的吗？ 
左师公曰： 今三世以前，至于赵主之子孙为侯者，其继有在者乎？ 
Left Master Gong says: If we go back three generations, up to the present, of all the sons of the rulers of Zhao who have been made marquises, which one of their heirs has succeeded to the throne?