"Doetsch and Bernstein, beginning from the early 1920s, worked together on the subject of Laplace transformation, integral equations and s. They published several papers together, in which the connection between the Laplace transformation and convolution, i.e., Faltung, is discussed often. ...[T]he Laplace transformation of a function f(t), denoted by \mathcal{L}(f), where f is defined for all real numbers t > 0, is the following complex function of F:F(t) = \mathcal{L}(f) = \int\limits_{0}^{\infty}e^{-tu} f(u)\, du.The relation between the Laplace transformation and convolution is...:\mathcal{L}(f*g) = \mathcal{L}(f) \cdot \mathcal{L}(g). ...In 1922, they remark, regarding the Laplace transformation: "[w]e distinguish the functions of a subfield and a field [Oberkörper], which are connected by a certain process. The operations in the subfield are actual, proper [eigentliche] ones, which are only symbolic in the field, but which in certain cases are capable of an actual analytical representation.""