Surface links with free abelian groups

抄録

It is known that if a classical link group is a free abelian group, then its rank is at most two. It is also known that a k-component 2-link group (k > 1) is not free abelian. In this paper, we give examples of T²-links each of whose link groups is a free abelian group of rank three or four. Concerning the T²-links of rank three, we determine the triple point numbers and we see that their link types are infinitely many.