1. Aschieri P., Blohmann C., Dimitrijevic M., Meyer F., Schupp P., Wess J.: A gravity theory on noncommutative spaces. Class. Quant. Grav. 22, 3511–3532 (2005)
2. Araki H.: On quasifree states of CAR and Bogoliubov automorphisms. Publ. Res. Inst. Math. Sci. Kyoto 6, 385–442 (1971)
3. Araki, H.: Mathematical Theory of Quantum Fields. Int. Series of Monographs on Physics. Oxford: Oxford University Press, 1999
4. Borchers H.-J., Buchholz D.: Global properties of vacuum states in de Sitter space. Annales Poincare Phys. Theor. A70, 23–40 (1999)
5. Bahns, D., Doplicher, S., Fredenhagen, K., Piacitelli, G.: Quantum Geometry on Quantum Spacetime: Distance, Area and Volume Operators. http://arxiv.org/abs/1005.2130v1 [hepth], 2010