It is a misfortune that an apparently full history of Greek geometry and astronomy, covering the period prior to 335 B.C., written by Eudemus pupil of Aristotle, has been lost. A brief account of this history was given later (ca. 450 A.D.) by Proclus, in his Commentary on Euclid. This abstract known the Eudemian Summary, constitutes our most reliable source o information for the very early period of Greek mathematics now under dis cussion. The account of the mathematical achievements of Thales, sketched in the preceding section, was furnished by Eudemian Summary