The Principle of Relativity and Special Relativity Triple
  Based on the principle of relativity and the postulate on universal invariant constants ($c,l$) as well as Einstein's isotropy conditions, three kinds of special relativity form a triple with a common Lorentz group as isotropy group under full Umov-Weyl-Fock-Lorentz transformations among inertial motions. 
Han-Ying Guo, Hong-Tu Wu and Bin Zhou