ABSTRACT
The equation (23.5) is the equation (14.11). The proof of the equation (14.12) is analogous. The equations (23.4) and (23.5) imply:
μi μj = 1. (23.7)
This and (23.6) verify (14.9). Since the point P is arbitrary, then it can also represent a light signal L, in which case (23.7) becomes:
μi μj = 1.
