 The extent of Leucippus' contribution to the developed atomist theory is unknown. His relationship to Democritus, and even his very existence, was a subject of considerable controversy in nineteenth century scholarship (Graham 2008). Most reports on early Greek atomism refer to the views of Democritus alone, or to both atomists together; Epicurus seems even to have denied that there was a philosopher Leucippus (DK 67A2). Aristotle certainly ascribes the foundation of the atomist system to Leucippus. Leucippus is sometimes said to have been the author of a work called the Great World-System; one surviving quotation is said to have come from a work On Mind. 