The Sulüzi 素履子 "Master with the straw sandals" is a philosophical treatise by the Tang period 唐 (618-907) scholar Zhang Hu 張弧. Of Zhang's life, nothing is known. In his book, he explains 14 terms known from Confucian philosophy, like virtue, loyalty, filial piety, and so on. The original book was only 1 juan "scroll" long, but the received version is divided into 3 juan. It had never attracted a wide readership and is not mentioned in contemporary bibliographies. The philosophical and literary level is not very high, and therefore is was only preserved in very few specimen after the Song period 宋 (960-1279). It has been included into the reprint series Siku quanshu 四庫全書, because it quotes from the Confucian classics. There is a print from the Ming period 明 (1368-1644) which was stored in the library of Ma Yujia 馬裕家 in the 18th century.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, vol. 2, p. 1548. Changchun: Jilin daxue chubanshe.