1. Andringa, R., Bergshoeff, E.A., Rosseel, J., Sezgin, E.: Newton-Cartan Supergravity; Classical Quant, Grav. 30, 205005 (2013). arXiv:1305.6737
2. Cartan E.: Sur les varietes a connexion affine et la theorie de la relativite. Ann EC. Norm. Sup. 40, 325–412 (1923)
3. Dautcourt G.: On the Newtonian limit of general relativity. Acta. Phys. Pol. B 21, 755 (1989)
4. Dunajski M.: Solitons, instantons & twistors, Oxford Graduate Texts in Mathematics. Oxford University Press, Oxford (2009)
5. Dunajski M.: The Twisted photon associated to hyper-hermitian four manifolds. J. Geom. Phys. 30, 266–281 (1999)