Of the writings of the Presocratics, only quotations embedded in the works of later authors have survived. These quotations, along with reports about the Presocratics and imitations of their works, were first compiled into a standard edition Die Fragmente der Vorsokratiker in the nineteenth century by Hermann Diels with revisions by Walther Kranz and subsequent editors, in a complete edition of all the works of Presocratic authors which has become standard in the field of ancient philosophy. The works of Presocratics, therefore, are normally referred to by DK numbers. Within each of these three groups, individual fragments or testimonia are assigned sequential numbers. So, for example, since Protagoras is the eightieth author in Diels-Kranz, the third testimony concerning him, a generally unreliable short biography by Hesychius, would be referred to as DK80a3.