The q-analogue of the wild fundamental group and the inverse problem of   the Galois theory of q-difference equations
  In previous papers, we defined $q$-analogues of alien derivations for linear analytic $q$-difference equations with integral slopes and proved a density theorem (in the Galois group) and a freeness theorem. In this paper, we completely describe the wild fundamental group and apply this result to the inverse problem in $q$-difference Galois theory. The new version contains an appendix on pronilpotent completion and the main result on the direct problem is made more precise. (Submitted for publication) 
Jean-Pierre Ramis and Jacques Sauloy
math.QA