Corners in non-equiregular sub-Riemannian manifolds
  We prove that in a class of non-equiregular sub-Riemannian manifolds corners are not length minimizing. This extends the results [4]. As an application of our main result we complete and simplify the analysis in [6], showing that in a 4-dimensional sub-Riemannian structure suggested by Agrachev and Gauthier all length-minimizing curves are smooth. 
Enrico Le Donne, Gian Paolo Leonardi, Roberto Monti, Davide Vittone
math.OC math.AP math.DG math.MG