In Example 6.2: AN(x,y) = x should read AN(x,y) = y.
Before Lemma 2: T≤M should read SN(>spo)≤M.
Proposition 5: polynomials in G and H must be of the form c x + d for some c ∈ {0, 1} and integer d. In addition, what is called linear polynomial over natural numbers in the surrounding text mean polynomials of this form.