Lickorish has constructed large
families of contractible 4-manifolds that have knotted embeddings in the 4-sphere
and has also shown that every finitely presented perfect group with balanced
presentation occurs as the fundamental group of the complement of a knotted
contractible manifold. Here we make a few observations regarding Lickorish’s
construction, showing how to extend it to construct contractible 4-manifolds which
have an infinite number of knotted embeddings and also to construct knotted
embeddings of the Mazur manifold for which the complement has trivial fundamental
group.