In [[non-standard analysis]], the '''standard part function''' is a function from the limited (finite) [[Hyperreal number|hyperrealshyperreal]] numbers to the realsreal numbers. Briefly, the standard part function "rounds off" a finite hyperreal to the nearest real. It associates to every such hyperreal, the unique real infinitely close to it. As such, it is a mathematical implementation of the historical concept of [[adequality]] introduced by [[Pierre de Fermat]].<ref>Karin Usadi Katz and [[Mikhail Katz|Mikhail G. Katz]] (2011) A Burgessian Critique of Nominalistic Tendencies in Contemporary Mathematics and its Historiography. [[Foundations of Science]]. {{doi|10.1007/s10699-011-9223-1}} [http://www.springerlink.com/content/tj7j2810n8223p43/] See [http://arxiv.org/abs/1104.0375 arxiv]. The authors refer to the Fermat-Robinson standard part.</ref> It can also be thought of as a mathematical implementation of [[Gottfried Wilhelm Leibniz|Leibniz]]'s [[Transcendental Law of Homogeneity]]. The standard part function was first defined by [[Abraham Robinson]]{{Citation needed|date=May 2011}} as a key ingredient in defining the concepts of the calculus, such as the derivative and the integral, in [[non-standard analysis]]. The latter theory is a rigorous formalisation of calculations with [[infinitesimal]]s. The standard part of ''x'' is sometimes referred to as its '''shadow'''.
