The Shiyaolun 世要論 "Treatise on important matters on earth" is a political treatise written by the Cao-Wei period 曹魏 (220-265) scholar Huan Fan 桓範 (died 249 CE). Huan Fan was Chamberlain for the national treasury (dasinong 大司農) and was killed by the general and regent Sima Yi 司馬懿. A book with the title of Zhengyaolun 政要論 "Treatise on important matters in politics" with a length of 12 juan "scrolls" is listed in the imperial bibliography Jingjizhi 經籍志 of the official dynastic history Suishu 隋書, among the legalist treatises. The bibliography in the Jiutangshu 舊唐書 calls it Daiyaolun 代要論 in order to avoid the personal name of Emperor Taizong 唐太宗 (r. 626-649), Li Shimin 李世民. There are many different titles for this book to be found in writings quoting from it, like Shiyaolun, Huan Fan xinshu 桓範新書 "New books by Huan Fan", Huan Fan shilun 桓範世論 "Huan Fan's treatise on the generations", Huangong shilun 桓公世論 "Sir Huan's treatise for the generations", 桓子 "Master Huan", Wei Huan Fan 魏桓範 "Fan Huan from Wei", Huan Fan lun 桓範論 "Huan Fan's treatise", or Huan Fan yaoji 桓範要集 "The important collection of Huan Fan". The title Shiyaolun corresponds to Huan Fan's own understanding of the book. The book was lost, yet the Qing period 清 (1644-1911) scholar Ma Guohan 馬國翰 reconstructed it as far as possible from quotations in Tang period 唐 (618-907) encyclopedias like the Beitang shuchao 北堂書鈔, Chuxueji 初學記 and Yiwen leiju 藝文類聚, the commentary to the anthology Wenxuan 文選, or the Song period encyclopedia Taiping yulan 太平御覽.
The Shiyaolun is included in the reprint series Yuhan shanfang jiyi shu 玉函山房輯佚書. A description can be found in the Xuxiu siku quanshu tiyao 續修四庫全書提要.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, vol. 2, p. 1642. Changchun: Jilin daxue chubanshe.