Combinatorial Approach to Milnor Invariants of Welded Links

For a classical link, Milnor defined a family of isotopy invariants, called Milnor mu-invariants. Recently, Chrisman extended Milnor mu-invariants to welded links by a topological approach. The aim of this paper is showing that Milnor mu-invariants can be extended to welded links by a combinatorial approach. The proof contains an alternative proof of the invariance of the original mu-invariants for clas-sical links.