 The first definition was made by Meijer using a series; nowadays the accepted and more general definition is via a line integral in the complex plane, introduced in its full generality by Arthur Erdélyi in 1953.With the modern definition, the majority of the established special functions can be represented in terms of the Meijer G-function.A notable property is the closure of the set of all G-functions not only under differentiation but also under indefinite integration.