The power of the four-dimensional symmetry of taiji relativity is demonstrated through an analysis of Edwards' transformation based on the weaker postulate that only the two-way speed of light is a universal constant. His transformation, involving Reichenbach's time, is shown to be inconsistent with Lorentz-group properties and the relativistic energy-momentum expression for particles. However, using the symmetry of taiji relativity as a guiding principle, we can obtain a new four-dimensional transformation which does not have these difficulties. We show that Reichenbach's concept of time is compatible with the four-dimensional symmetry of physical laws. No known experiments can distinguish physical laws in this four-dimensional formalism («extended relativity») from those in special relativity.