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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 $\Delta$.