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I read on some encyclopedias that there was a historical school that had the Mahaparinirvana Sutra as its main text and was called Niepanshi 涅槃師 or Nieh-p’an-tsung/ Niepan zong in chinese and Nehan-shu in japanese (est. in the 4-5th century). On the wiki page on Korean Buddhism its written that there was a school called Yeolban (涅槃宗). It seems that it faded away and got extinct at some point and absorbed into other traditions.
Now where can I read what their rituals were and which sutras they used in their liturgy? There has to be information (historically) about their beliefs, interpretations, their patriarchs, lineage and commentaries. Is there any scholarly work?