Derivatives of Links: Milnor's Concordance Invariants and Massey's Products

Book excerpt: We investigate higher-order cohomology operations (Massey products) on complements of links of circles in [italic]S3. These are known to be essentially equivalent to the [lowercase Greek]Mu [with macron]-invariants of John Milnor, which detect whether or not the longitudes of the link lie in the [italic]n[superscript]th term of the lower central series of the fundamental group of the link compliment. We define a geometric "derivative" on the set of all links and use this to define higher-order linking numbers which are shown to be "pieces" of Massey products.