They represent different periods of Chinese-American history.

VOA: special.2010.03.03

When these tyrannies take place, they last for different periods of time, but when the tyrant is removed, what follows after that is, there is never again in that town a one-man rule of any kind.

当僭主统治步入历史舞台,它走过了很多历史时期,但当它寿终正寝之后,在那座城邦里再也没有出现过,任何形式的独裁者了

耶鲁公开课 - 古希腊历史简介课程节选

So now there is a problem of credibility of what the government is going to do, and of course the situation is different to situations in other periods because now there is a common currency."

VOA: standard.2010.06.24