1. G.W. Gibbons and S.W. Hawking (eds.): Euclidean Quantum Gravity, (World Scientific, 1993).
2. R. Penrose: The Emperor’s New Mind, (Oxford University Press, 1989).
3. D. Kastler (ed.): Quantum Groups, Non-Commutative Geometry and Fundamental Physical Interactions, (Nova Science Publishers, 1999); see also, D. Kastler: Cyclic Cohomology within the Differential Envelope, (Herman, Paris, 1988).
4. S. Albeverio, J. Jost, S. Paycha and S. Scarlatti: A Mathematical Introduction to String Theory, (LNM225, Cambridge University Press, 1997).
5. R. Penrose: Singularities and Time-Asymmetry. In: General Relativity: An Einstein Centenary Survey, S.W. Hawking and W. Israel (eds.), (Cambridge University Press, 1979).