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
Elements of Algebra Elements of Algebra Elements of Algebra is an elementary mathematics textbook written by mathematician Leonhard Euler and originally published in 1770 in German. "Elements of Algebra" is one of the earliest books to set out algebra in the modern form we would recognize today (another early book being "Elements of Algebra" by Nicholas Saunderson, published in 1740), and is one of Euler's few writings, along with "Letters to a German Princess", that are accessible to the general public. Written in numbered paragraphs as was common practice till the 19th century, "Elements" begins with the definition of mathematics and builds on