  We begin by admitting the following: (i) there is a frame of reference where
the speed of light is the same in any direction (that speed is c) (ii) the
average speed of light on a two-way journey is c in every frame of reference.
  From this two premises we obtain an expression for the speed of light which
implies the speed of light depends on the motion of the frame of reference.
Also from this two premises solely we deduct Lorentz Transformation.
