Guiding to "Zhonghe"of YE Shi;

The sayings,"Whereas the force of words is soon spent,far better is it to guard medium" and "It is constant to empty the self completely;it is sincere to guard medium",fully reflect the "guarding medium" of Lao Tzu.

Tang’s Border Area Control Policies Seeing from Tomb Inscriptions of Pei Huaigu, Li Shizi and He Shouyang;