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Location: Chapter 25, Problem 2 (last paragraph)

It is

We now need a bird \(\Delta\) called a normalizer such that for every number \(n\), \(\Delta\,n = \overline{n \star n^\#}\).

It should become

We now need a bird \(\Delta\) called a normalizer such that for every number \(n\), \(\Delta\,\overline{n} = \overline{n \star n^\#}\).

Short explanation

The Normalizer bird, like any other bird, can be applied not to numbers (in the sense of elements of \(\mathbb{N}\)), but only to numerical birds. Hence the need for an overlined symbol after the \(\Delta\).