《汉书·志·艺文志》
所以说《易》的道理是很深刻的，经历了伏羲、文王、孔子三代圣人，经历了上、中、下三个远古时代。
故曰《易》道深矣，人更三圣，世历三古。
So Yijing is very profound, it spent three generation of sagely men, Fuxi, King Wen and Confucius, it spent three ancient eras, the ancient, the middle and the newest.