sentences:  The Tang dynasty founder Emperor Gaozu initially followed the Sui's system of governance, including the five-bureau organization.However, he deviated from his predecessors by creating a single head for the executive bureau, known as the "Shàngshūlǐng" (尚書令) and appointed the office to his second son and future emperor Lǐ Shìmín (李世民).After Li Shimin became emperor in 626, the office was left vacant because none of his officials dared to occupy it.