The Whitehead link, the Borromean rings and the knot 9 are universal.
A link L in S is universal if every closed, orientable 3-manifold is a covering of S branched over L. Thurston [1] proved that universal links exist and he asked if there is a universal knot, and also if the Whitehead link and the Figure-eight knot are universal. In [2], [3] we answered the first question by constructing a universal knot. The purpose of this paper is to prove that the Whitehead link and the Borromean rings, among others, are universal. The question about the Figure-eight knot remains...