Link Groups and Galois Groups with Restricted Ramification

As explained in Chap. 3 , our basic idea is to regard a Galois group with restricted ramification \(G_{S} = \pi _{1}(\mathrm {Spec}(\mathbb {Z}) \setminus S)\) , \(S = \{ p_{1},\cdots ,p_{r} \}\) , as an analogue of a link group \(G_{L} = \pi _{1}(S^{3} \setminus L), L = K_{1}\cup \cdots \cup K_{r}\) (cf. ( 3.11 )).