It is easily shown: first, that every [neuron] net, if furnished with a tape, scanners connected to afferents, … Turing machine; second, that each of the latter … [i.e., cyclic] can be computed by such a net; and that nets … but no others, and not all of them. … its equivalents, Church's \lambda-definability and Kleene's primitive recursiveness: … conversely.
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