===Infinitesimal===
Inherent in the concept of infinity is the concept of infinitesimal: infinity small. [[Archimedes]] used small numbers and areas, as in calculating the area under a parabola, but the [[Ancient Greeks]] rejected the concept of infinity. Beginning with the 17th century, mathematicians like [[Fermat]], [[Euler]], [[Newton]], and [[Leibniz]] used the concept of infinitesimal in integrals and differentials. [[Bernhard Riemann]] used the concept of infinitesimal limits to develop a rigorous definition of the integral, now known as the [[Riemann Integral]].
=== Infinity and economics ===