Doubly-Special Relativity: First Results and Key Open Problems by
Amelino-Camelia.
I can figure out the gist - they are looking for a way to maintain the
Principle of Relativity which making a bridge to Quantum Gravity theories.
Part of the problem is to figure out what the frame-independent quantity
needs to be in order to derive the further stage of "Lorentz"
transformations. The author says that Einstein had it easy because it was
fairly obvious that it had to be c for the first stage.
Especially after the recent thread on the logical status of SR, I'd
interested to read what people think of all this.
Mark.
PS The link to the pdf wouldn't open with my W98/Mozilla browser, but
opened instantly with my Linux/Mozilla combination.