Parallel (geometry) as a pair of straight lines in a plane which do not meet appears as Definition 23 in Book I of Euclid's Elements. Alternative definitions were discussed by other Greeks, often as part of an attempt to prove the parallel postulate. Proclus attributes a definition of parallel lines as equidistant lines to Posidonius and quotes Geminus in a similar vein. Simplicius also mentions Posidonius' definition as well as its modification by the philosopher Aganis. At the end of the nineteenth century, in England, Euclid's Elements was still the standard textbook in secondary schools. The traditional treatment of geometry was being
Library of Alexandria the "Letter of Aristeas" is very late and it contains information that is now known to be inaccurate. Other sources claim that the Library was instead created under the reign of Ptolemy I's son Ptolemy II Philadelphus (283–246 BC). Modern scholars agree that, while it is possible that Ptolemy I may have laid the groundwork for the Library, it probably did not come into being as a physical institution until the reign of Ptolemy II. By that time, Demetrius of Phalerum had fallen out of favor with the Ptolemaic court and could not, therefore, have had any role in establishing