... reproduction¹

Also often called simply ``replication''.

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... tape);²

This is as von Neumann formulated his design, but it may be noted that nothing important hangs on the constructor having this double functionality; the tape copying could be mediated by completely separate machinery, or even no machinery at all, without materially affecting any of the analysis which follows.

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... phenotype.³

Of course, this encoding must be relative to the particular decoding implemented by the parental constructor. We will return to this point shortly.

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... unlimited.⁴

Admittedly, this ease of interaction actually makes the problem of realising ``quasi-quiescence'' rather harder--because any given program entity can effectively disrupt any other. This seriously constrained evolutionary phenomena in earlier systems of this sort, such as the $\alpha$-universes (McMullin, 1992; Holland, 1976) or Coreworld (Rasmussen et al., 1990). Perhaps the most important innovation in the development of Tierra was the introduction of ``memory protection'' which allowed for control of such interactions.

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