The boundaries of some classes in ancient Chinese are not very clear. As far as names are concerned, some names are the same but different from each other: the preface and postscript order is completely different from the gift order; Motto and epitaph inscriptions are also completely different. As far as content is concerned, some works may cross categories. For example, although Jia Yi's "On Accumulation and Storage" belongs to the commemorative category, it is full of discussion, much like prose; Although Han Yu's Preface to Send Meng Dongye belongs to the category of giving preface, it is full of reasoning, much like an essay. Yang Xiong's Jie Chao and Xiao Tong's Selected Works classify it as "hypothesis", while Wen Gu's Ci Tan Lei belongs to Ci Fu, because it belongs to argumentative writing in content and Ci Fu in form. Han Yu's "Jin Xuejie" is modeled after the genre of "Jiechao", and Wen Gu Ci Tan Lei also classifies it as a ci.