Theon of Alexandria in Wikipedia

Theon (Greek: Θέων; ca. 335 – ca. 405) was a Greek[1] scholar and mathematician who lived in Alexandria, Egypt. He edited and arranged Euclid's Elements and Ptolemy's Handy Tables, as well as writing various commentaries. Theon was the father of Hypatia who also won fame as a mathematician. Life The biographical tradition (Suda) defines Theon as "the man from the Mouseion"; actually, both the Library of Alexandria and the Mouseion may have been destroyed a century before by the Emperor Aurelian during his struggle against Zenobia. Some scholars think that they were closed by the patriarch Theophilus on order of the Christian Roman emperor Theodosius I in 391. Theon was the father of the mathematician Hypatia whose murder was attributed by Socrates Scholasticus to "political jealousy" which instigated mob violence. Works Theon's most durable achievement may be his edition of Euclid's Elements, published around 364 and authoritative into the 19th century. The bulk of Theon's work, however, consisted of commentaries on important works by his Hellenistic predecessors. These included a "conferences" (Synousiai) on Euclid, and commentaries (Exegeseis) on the Handy Tables and Almagest of Ptolemy, and on the technical poet Aratus. In one of the commentaries on the Handy Tables, Theon states that certain (unnamed) ancient astrologers believed that the precession of the equinoxes, rather than being a steady unending motion, instead reverses direction every 640 years, and that the last reversal had been in 158 BC.[2] Theon describes but did not endorse this theory. This idea inspired Thābit ibn Qurra in the 9th century to create the theory of trepidation to explain a variation which he (incorrectly) believed was affecting the rate of precession.[2]