Normal forms for sub-Lorentzian metrics supported on Engel type distributions (Q2442606)

The author constructs normal forms for Lorentzian metrics on Engel distributions under the assumption that abnormal curves are time-like future directed Hamiltonian geodesics. Then he indicates some cases in which the abnormal time-like future directed curve initiating at the origin is geometrically optimal. He also gives certain estimates for reachable sets from a point.