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
Political and military events in Scotland during the reign of David I of Scotland and England", a title which acknowledged the new Scoto-Northumbrian identity of David's realm. Political and military events in Scotland during the reign of David I Political and military events in Scotland during the reign of David I are the events which took place in Scotland during David I of Scotland's reign as King of Scots, from 1124 to 1153. When his brother Alexander I of Scotland died in 1124, David chose, with the backing of Henry I of England, to take the Kingdom of Alba for himself. David was forced to engage in warfare against his rival and