The isochronous center problem for polynomial systems is an open problem .

时间可逆多项式系统的等时中心问题是一类公开问题.

The dissolution of hu-han contexts is not an isochronous progress together with the flourishing and perdition of a dynasty ; on the one hand it is a natural result of national conflicts and amalgamations ; on the other hand , the evolvement of human 's notions is a vital factor of the dissolution .

它一方面是民族冲突与民族融合进程的自然结果；另一方面，在特定历史背景下，人们观念与认识的演变也是促成这种“消解”的重要因素。