 Sima Qian, in his "Shiji", equates the popularity of the "Wuzi", in both the Warring States and the Han dynasty, with that of Sun Tzu's Art of War.There is evidence that, in the Warring States, two different texts titled ""Wuzi"" existed, but (at least) one of them has been lost.The fact that large portions of the text seem to have been either lost or deliberately excised from surviving editions makes the dating of the work more challenging.