 His "Compendious Book on Calculation by Completion and Balancing" presented the first systematic solution of linear and quadratic equations in Arabic.Gerbert of Aurillac marked triples of columns with an arc (called a "Pythagorean arc") when using his Hindu–Arabic numeral-based abacus in the 10th century.Fibonacci followed this convention when writing numbers such as in his influential work "Liber Abaci" in the 13th century.