1. A. Sobel, Scientific American, Vol. 22, No. 6, 65 (1973).
2. G. Heilmeier, Scientific American, Vol. 222, No. 4, 100 (1970).
3. R. A. Soref, Appl. Optics 9:1323 (1970).
4. N. J. Murrell, U.S. Patent 3,959,963 (1976).
5. S. Sherr, IEEE Conf. on Display Devices 52 (1972).