On the Spherical Hausdorff Measure in Step 2 Corank 2 sub-Riemannian   Geometry
  In this paper, we consider generic corank 2 sub-Riemannian structures, and we show that the Spherical Hausdorf measure is always a C^1-smooth volume, which is in fact generically C^2- smooth out of a stratified subset of codimension 7. In particular, for rank 4, it is generically C^2 . This is the continuation of a previous work by the auhors. 
Ugo Boscain (CMAP), Jp Gauthier (LSIS)
math.DG