1. R. Arnowitt, S. Deser and C.W. Misner, in: Gravitation, an introduction to current research, L. Witten ed., Wiley 1962.
2. P.A.M. Dirac, “Lectures on quantum mechanics”, Yeshiva University Press 1964.
3. A. Ashtekar and M. Streubel, Proc. R. Soc. Lond. A376 (1981) 585–607.
4. A. Ashtekar and A. Magnon-Ashtekar, Comm. Math. Phys. 86 (1982) 55–68.
5. A. Ashtekar, in General relativity and gravitation, vol. 2, A. Held ed., Plenum 1980.