Existence of tangent lines to Carnot-Carath\'eodory geodesics
  We show that length minimizing curves in Carnot-Carath\'eodory spaces possess at any point at least one tangent curve (i.e., a blow-up in the nilpotent approximation) equal to a straight horizontal line. This is the first regularity result for length minimizers that holds with no assumption on either the space (e.g., its rank, step, or analyticity) or the curve, and it is novel even in the setting of Carnot groups. 
Roberto Monti, Alessandro Pigati and Davide Vittone
math.OC math.MG