Liouville's theorem (differential algebra)
In mathematics, Liouville's theorem, originally formulated by French mathematician Joseph Liouville in 1833 to 1841, places an important restriction on antiderivatives that can be expressed as elementary functions. The antiderivatives of certain elementary functions cannot themselves be expressed as elementary functions.
Source: Wikipedia — Liouville's theorem (differential algebra) (CC BY-SA 4.0)