Systems theory to social sciences (see David Easton's seminal development of the "political system" as an analytical construct), the original theorists explored the implications of twentieth century advances in terms of systems. People have studied subjects like complexity, self-organization, connectionism and adaptive systems in the 1940s and 1950s. In fields like cybernetics, researchers such as Norbert Wiener, William Ross Ashby, John von Neumann and Heinz von Foerster, examined complex systems mathematically. John von Neumann discovered cellular automata and self-reproducing systems, again with only pencil and paper. Aleksandr Lyapunov and Jules Henri Poincaré worked on the foundations of chaos theory without any computer
Paley–Wiener integral Paley–Wiener integral In mathematics, the Paley–Wiener integral is a simple stochastic integral. When applied to classical Wiener space, it is less general than the Itō integral, but the two agree when they are both defined. The integral is named after its discoverers, Raymond Paley and Norbert Wiener. Let "i" : "H" → "E" be an abstract Wiener space with abstract Wiener measure "γ" on "E". Let "j" : "E" → "H" be the adjoint of "i". (We have abused notation slightly: strictly speaking, "j" : "E" → "H", but since "H" is a Hilbert space, it is isometrically isomorphic to