Hillman, Jonathan A. Abelian normal subgroups of two-knot groups. (English) Zbl 0611.57015 Comment. Math. Helv. 61, 122-148 (1986). For \(n\neq 2\) it is known which abelian groups can appear as subgroups of the centre of an n-knot group. An earlier paper of the author [ibid. 56, 465-473 (1981; Zbl 0478.57016)] considered the case of \(n=2\), but a gap was later found in the proof of a key lemma. The present paper fills that gap, and considers the more general question of abelian normal subgroups of 2-knot groups. It is shown that if such a subgroup is torsion free and of rank \(r>1\), then the knot group is an orientable Poincaré duality group of formal dimension 4, and so \(r\leq 4.\) The cases \(r=3\), 4 are settled completely, whilst many examples for \(r=1\), 2 can be constructed by twist-spinning classical knots. However, as the author points out, there are examples of 2-knot groups with rank 1 abelian normal subgroups which cannot be realized by fibred knots. He goes on to show that any virtually solvable 2-knot group must be either virtually poly-\({\mathbb{Z}}\) or an example given by R. H. Fox which has commutator subgroup the dyadic rationals or admit no nontrivial torsion free abelian normal subgroup. Reviewer: Ch.Kearton Cited in 2 ReviewsCited in 7 Documents MSC: 57Q45 Knots and links in high dimensions (PL-topology) (MSC2010) Keywords:centre of an n-knot group; abelian normal subgroups of 2-knot groups; Poincaré duality group; fibred knots; virtually solvable 2-knot group Citations:Zbl 0478.57016 PDFBibTeX XMLCite \textit{J. A. Hillman}, Comment. Math. Helv. 61, 122--148 (1986; Zbl 0611.57015) Full Text: DOI EuDML