1. Penrose R.: A Brief Outline of Twistor Theory. University of Oxford preprint, 1980.
2. We are adopting the notation of Penrose's school: spinor indices, unprimed or primed, are chosen from capital Roman letters, and they take the values 0 and 1 or 0′ and 1′. An overbar means complex conjugation. The complex conjugation of spinors converts unprimed indices into primed ones andvice versa. The complex conjugation of twistors displaces both Greek twistor indices and Roman lower case constituent indices. We do not pay attention to the order of different kinds of indices. We denote, however, symmetrization in like indices by enclosing the indices in parentheses. The transformation from spinor coordinatesxAA′ to the time coordinate of the familiar orthogonal coordinate system proceedst= 1/√2 (x00′+x11′).
3. Penrose R.:in Quantum theory and the structure of time and space (Eds. L. Castell, M. Drieschner and C. F. von Weizsäcker) Carl Hanser, München, 1975.
4. Perjés Z.: Phys. Rev. D20 (1979) 1857.
5. Hughston L. P.: Twistors and particles, Lecture notes in Physics, Vol. 97. Springer, Berlin, 1979.