The good regulator is a theorem conceived by Roger C. Conant and W. Ross Ashby that is central to cybernetics. Originally stated that "every good regulator of a system must be a model of that system",[1] but more accurately, every good regulator must contain a model of the system. That is, any regulator that is maximally simple among optimal regulators must behave as an image of that system under a homomorphism; while the authors sometimes say 'isomorphism', the mapping they construct is only a homomorphism.