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.