sentences:  After Emperor Xuanzong ascended the throne, he gave the title "Prince of Sui" (遂王) to Ningjiasu.Emperor Xuanzong's eldest son and heir apparent, Wanyan Shouzhong (完顏守忠), as well as Wanyan Shouzhong's son, both died prematurely, so in 1216 Emperor Xuanzong declared Ningjiasu, his next oldest surviving son, as his heir apparent.Ningjiasu chose for himself the sinicized name "Shouxu" (守緒).