  It is proved that local Lorentz transformations for different systems cannot
derive varying speed of light. Based on the special relativity principle, an
invariant speed is necessarily obtained. Therefore, the exact basic principles
of the special relativity should be redefined as: I. The special relativity
principle, which derives necessarily an invariant speed. II. Suppose that the
invariant speed in the theory is the speed of light in the vacuum c. If the
second principle does not hold, for example, the superluminal motions exist,
the theory will be still the extensive special relativity, in which the
formulations are the same, only c is replaced by the invariant speed. If the
invariant speed are various invariant velocities, the diversity of space-time
will correspond to many worlds. Varying speed of light theory is probably
connected only with the general relativity.
