The Niepan zong， or Nirva^na Sutra School. One of the so-called "thirteen sects 十三宗" of China. This school， centering on the teachings contained in the Maha^ya^na Nirva^na-sutra 涅槃经，advocated such doctrines as the eternal existence of the dharma-body 法身 and the presence of the buddha-nature 佛性 in all sentient beings. Once the Northern edition of the sutra arrived in Honan， Tao-sheng 道生， who had been criticized for his denouncement of icchantika 一阐提 theory， was vindicated. Studies of the sutra then began to flourish， and the southern Nirvana Sutra school came into being. Hui-kuan postulated the teaching classification 判教 of five periods of sudden and gradual 顿渐五时， placing the content of the Nirvana Sutra as reflecting the most complete expression of the Buddha's instruction. The peak of the Nirvana school was during the period of the northern and southern courts （439-589）. After the time of the Sui， commentarial works on the sutra were written by such eminent figures as Huiyuan 慧远， Chi-tsang 吉藏， and Kuan-ting 灌顶， but it began to be phased out as a separate entity with the appearance of the Samgraha 摄论宗 and Tiantai 天台宗 schools. It almost fully disappeared during the T'ang， especially after the appearance of the Sanlun 三论宗， Faxiang 法相宗 and Huayan 华严宗 schools， but its basic doctrines were deeply assimilated by these successor traditions. The Nirvana school tradition was also transmitted to Korea and Japan， where it held significant influence..