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On the space of null geodesics of a spacetime: the compact case, Engel geometry and retrievability. (arXiv:2112.06955v1 [math.DG]) http://arxiv.org/abs/2112.06955
On the space of null geodesics of a spacetime: the compact case, Engel geometry and retrievability. (arXiv:2112.06955v1 [math.DG]) http://arxiv.org/abs/2112.06955