Multivariable Alexander Polynomial

Let L be a link with n components and let X denote the universal abelian cover of S3 - L. The first homology H1(X) of X may be expressed as a Z[t1±, ..., tn±] module. This is called the Alexander module of L, denoted A(L). The multivariable Alexander polynomial Δ(L) of L is the order of A(L), and is unique up to multiplication by ±1, ±t1, ..., ±tn±.