 How strong this result is becomes clear when we analyze the class of Turing complete systems in more detail. In the first half of the twentieth century three fundamentally different proposals for a general theory of computation were formulated: Gödel’s recursive functions ( Gödel 1931), Turing’s automata (Turing 1937) and Church’s Lambda Calculus (Church 1936). Each of these proposals in its own way clarifies aspects of the notion of computing. Later much more examples followed. The class of Turing equivalent systems is diverse. Apart from obvious candidates like all general purpose programming languages (C, Fortran, Prolog, etc.) it also contains some unexpected elements like various games (e.g., Magic: The Gathering [Churchill 2012  OIR]).  The table below gives an overview of some conceptually interesting systems: 