Editing Leonhard Euler (section)

===Mathematical notation===
Euler introduced and popularized several notational conventions through his numerous and widely circulated textbooks. Most notably, he introduced the concept of a [[function (mathematics)|function]]{{sfn|Dunham|1999|p=17}} and was the first to write ''f''(''x'') to denote the function ''f'' applied to the argument ''x''. He also introduced the modern notation for the [[trigonometric functions]], the letter {{math|''e''}} for the base of the [[natural logarithm]] (now also known as [[Euler's number]]), the Greek letter [[Sigma|Σ]] for summations and the letter {{math|''i''}} to denote the [[imaginary unit]].<ref name=Boyer/> The use of the Greek letter ''[[pi (letter)|π]]'' to denote the [[pi|ratio of a circle's circumference to its diameter]] was also popularized by Euler, although it originated with [[Welsh people|Welsh]] mathematician [[William Jones (mathematician)|William Jones]].<ref name=arndt/>