An Approach to Homotopy Classification of Links
J. P. Levine · Transactions of the American Mathematical Society · 1988
A reformulation and refinement of the $\overline \mu$-invariants of Milnor are used to give a homotopy classification of $4$ component links and suggest a possible general homotopy classification. The main idea is to use the (reduced) group of a link and its "geometric" automorphisms to define the precise indeterminacy of these invariants.