춘추좌씨전
The "Zuo Zhuan" originally contained only its core content, without any content from or references to the "Spring and Autumn Annals". In the 3rd century AD, the Chinese scholar Du Yu intercalated the "Annals" into the "Zuo Zhuan", producing the received format that exists today. The entries follow the strict chronological format of the "Annals", so interrelated episodes and the actions of individual characters are sometimes separated by events that occurred in the intervening years. Each "Zuo zhuan" chapter begins with the "Spring and Autumn Annals (Chunqiu)" entry for the year, which is usually terse and brief, followed by the "Zuo Zhuan" content for that year, which often contains long and detailed narratives.