Chapter 12: The Principle of Computational Equivalence

Section 3: The Content of the Principle

Encodings [for universality]

One can prevent an encoding from itself introducing universality by insisting, for example, that it be primitive recursive (see page 907) or always involve only a bounded number of steps. One can also do this—as in the rule 110 proof in the previous chapter—by having programs and data be encoded separately, and appear, say, as distinct parts of the initial conditions for the system one is studying. (See also page 1118.)

From Stephen Wolfram: A New Kind of Science [citation]