1. Coll, B., 2006, in Proceedings of the XXVIII Spanish Relativity Meeting ERE-2005 on A Century of Relativity Physics, AIP Conf. Proc. (New York: AIP), 277, see also [gr-qc/0601110]
2. Coll, B., Ferrando, J.J., Morales, J.A., 2007, on Newtonian frames [arXiv:0707.0248]
3. 199 Causal classes of space-time frames
4. Relativistic positioning systems: the emission coordinates