Knotted contractible 4-manifolds in the 4-sphere
arXiv:math/0107227
Abstract
Examples are given to show that some compact contractible 4-manifolds can be knotted in the 4-sphere. It is then proved that any finitely presented perfect group with a balanced presentation is a knot group for an embedding of some contractible 4-manifold in the 4-sphere.
Six pages with two figures