Non-Euclidean geometry that are both perpendicular to a third line: Euclidean geometry, named after the Greek mathematician Euclid, includes some of the oldest known mathematics, and geometries that deviated from this were not widely accepted as legitimate until the 19th century. The debate that eventually led to the discovery of the non-Euclidean geometries began almost as soon as Euclid's work "Elements" was written. In the "Elements", Euclid began with a limited number of assumptions (23 definitions, five common notions, and five postulates) and sought to prove all the other results (propositions) in the work. The most notorious of the postulates is often
Pope Dioscorus I of Alexandria Coptic Orthodox and Greek Orthodox Patriarchates of Alexandria agreed to mutually recognize baptisms performed in each other's churches. Pope Dioscorus I of Alexandria Pope Dioscorus I of Alexandria, 25th Pope of Alexandria & Patriarch of the See of St. Mark. He was deposed by the Council of Chalcedon in 451 but was recognized as Patriarch by the Coptic Church until his death. He died on the Island of Gangra, Paphlagonia, in September 454. He is venerated as a saint by the Coptic and other Oriental Orthodox churches. Dioscorus served as the dean of the Catechetical School of Alexandria, and was