Solvable normal subgroups of 2-knot groups
Abstract
If X is an orientable, strongly minimal PD4-complex and π1(X) has one end, then it has no nontrivial locally finite normal subgroup. Hence, if π is a 2-knot group, then (a) if π is virtually solvable, then either π has two ends or π≅Φ, with presentation 〈a,t|ta=a2t〉, or π is torsion-free and polycyclic of Hirsch length 4 (b) either π has two ends, or π has one end and the center ζπ is torsion-free, or π has infinitely many ends and ζπ is finite, and (c) the Hirsch–Plotkin radical √π is nilpotent.