# Happy Integral Day!

From Wikipedia:

According to Leibniz’s notebooks, a critical breakthrough occurred on 11 November 1675, when he employed integral calculus for the first time to find the area under the function y = x. He introduced several notations used to this day, for instance the integral sign ∫ representing an elongated S, from the Latin word summa and the d used for differentials, from the Latin word differentia.

$int x, {rm d}x=frac{1}{2}x^2$, for those not in the know.