The Art of War by active 6th century B.C. Sunzi

4. TU YU (died 812) did not publish a separate commentary on Sun Tzŭ,

his notes being taken from the _T’ung Tien_, the encyclopedic treatise on the Constitution which was his life-work. They are largely repetitions of Ts’ao Kung and Meng Shih, besides which it is believed that he drew on the ancient commentaries of Wang Ling and others. Owing to the peculiar arrangement of _T’ung Tien_, he has to explain each passage on its merits, apart from the context, and sometimes his own explanation does not agree with that of Ts’ao Kung, whom he always quotes first. Though not strictly to be reckoned as one of the "Ten Commentators," he was added to their number by Chi T’ien-pao, being wrongly placed after his grandson Tu Mu.