Foundations of geometry possible exception of the parallel postulate) that any theorem proved from them was deemed true in an absolute, often metaphysical, sense. Today, however, many other geometries which are not Euclidean are known, the first ones having been discovered in the early 19th century. Euclid's "Elements" is a mathematical and geometric treatise consisting of 13 books written by the ancient Greek mathematician Euclid in Alexandria c. 300 BC. It is a collection of definitions, postulates (axioms), propositions (theorems and constructions), and mathematical proofs of the propositions. The thirteen books cover Euclidean geometry and the ancient Greek version of elementary number theory.
Cosmas I of Alexandria Cosmas I of Alexandria Cosmas I or Kosmas I () served as Greek Patriarch of Alexandria between ca. 727 and his death in 768. Cosmas was the first residential Chalcedonian (Melkite) patriarch to be established in Alexandria following the Muslim conquest of Egypt in the 640s. The see had remained vacant since, but Cosmas was appointed with the consent of both the Umayyad Caliph and the Byzantine Emperor. The chronicler Theophanes the Confessor reports that in 742/3, he abjured Monotheletism, the dominant doctrine among Alexandrian Melkites since it had been promulgated by Emperor Heraclius. As Cosmas himself was most likely