@article{nieto_león_2010,  title={2d Gravity with torsion, oriented matroids and 2+2 dimensions},  volume={40},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332010000400004},  DOI={10.1590/S0103-97332010000400004},  number={4},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Nieto, J.A. and León, E.A.},  year={2010},  month={Dec},  pages={383–387} }