1. Arnold V.I. (ed.) (1988) Dynamical Systems III. Springer, Berlin
2. DeWitt, B.S.: The Quantization of geometry. In: Witten, L. (ed.) (1962) Gravitation: An Introduction to Current Research. Wiley, New York (1962)
3. DeWitt B.S. (1967). Phys. Rev. 160: 1113
4. Dittrich, B.: Partial and complete observables for canonical general relativity. Class. Quant. Grav. 23, 6155 (2006). E-print: gr-qc/0507106
5. Dittrich, B., Tambornino, J.: A perturbative approach to Dirac observables and their space–time algebra. Class. Quant. Grav. 24, 757 (2007). E-print: gr-qc/0610060