1. Hassaïne, M., Troncoso R., Zanelli, J.: Eleven-dimensional supergravity as a gauge theory for the M-algebra. Phys. Lett. B 596, 132 (2004)
2. Bandos, I.A., de Azcárraga, J.A., Izquierdo, J.M., Lukierski, J.: BPS states in M-theory and twistorial constituents. Phys. Rev. Lett. 86, 4451 (2001)
3. Bandos, I.A., de Azcárraga, J.A., Izquierdo, J.M., Picon, M., Varela, O.: BPS preons, generalized holonomies and 11D supergravities. Phys. Rev. D 69, 105010 (2004)
4. Gran, U., Gutowski, J., Papadopoulos, G., Roest, D.: N = 31, D = 11. JHEP 0702, 043 (2007)
5. Teitelboim, C.: Quantum mechanics of the gravitational field. Phys. Rev. D 25, 3159 (1982)