二序

The two kinds of introductory phrase: (a) the ordinary opening phrase of a sutra-- "Thus have I heard"; and (b) specific openings referring to the circumstances in which the sūtra was produced.

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諸經開頭時， 有通序和別序。 如是我聞等是共通於諸經都有， 叫通序， 序說本經特殊的緣起， 叫別序。