Editing Integral (section)

=== Historical notation ===
The notation for the indefinite integral was introduced by [[Gottfried Wilhelm Leibniz]] in 1675.<ref>{{Harvnb|Burton|2011|loc=p.&nbsp;414}}; {{Harvnb|Leibniz|1899|loc=p.&nbsp;154}}.</ref> He adapted the [[integral symbol]], '''∫''', from the letter ''ſ'' ([[long s]]), standing for ''summa'' (written as ''ſumma''; Latin for "sum" or "total"). The modern notation for the definite integral, with limits above and below the integral sign, was first used by [[Joseph Fourier]] in ''Mémoires'' of the French Academy around 1819–1820, reprinted in his book of 1822.<ref>{{Harvnb|Cajori|1929|loc=pp.&nbsp;249–250}}; {{Harvnb|Fourier|1822|loc=§231}}.</ref>

[[Isaac Newton]] used a small vertical bar above a variable to indicate integration, or placed the variable inside a box. The vertical bar was easily confused with {{math|{{overset|'''.'''|''x''}}}} or {{math|''x''′}}, which are used to indicate differentiation, and the box notation was difficult for printers to reproduce, so these notations were not widely adopted.<ref>{{Harvnb|Cajori|1929|p=246}}.</ref>