Extremal curves in nilpotent Lie groups
  We classify extremal curves in free nilpotent Lie groups. The classification is obtained via an explicit integration of the adjoint equation in Pontryagin Maximum Principle. It turns out that abnormal extremals are precisely the horizontal curves contained in algebraic varieties of a specific type. We also extend the results to the nonfree case. 
Enrico Le Donne, Gian Paolo Leonardi, Roberto Monti, Davide Vittone
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