Diels–Kranz (DK) numbering is the standard system for referencing the works of the ancient Greek pre-Socratic philosophers, based on the collection of quotations from and reports of their work, Die Fragmente der Vorsokratiker (The Fragments of the Pre-Socratics), by Hermann Alexander Diels. The Fragmente was first published in 1903, was later revised and expanded three times by Diels, and was finally revised in a fifth edition (1934–7) by Walther Kranz and again in a sixth edition (1952). In Diels-Kranz, each passage, or item, is assigned a number which is used to uniquely identify the ancient personality with which it is concerned, and the type of item given. Diels-Kranz is used in academia to cite pre-Socratic philosophers, and the system also encompasses Sophists and pre-Homeric poets s