i find in the literature 1. space is homogeneous and isotropic and time homogeneous, at least if judged by observers at rest in S(0). 2. in the isotropic system S(0) the velocity of light is "c" in all directions, so that clocks can be synchronized in S(0) and one way velocities relative to S(0) can be measured. 3. the two way velocity of light is the same in all directions in all inertial systems. 4. clock retardation takes place with the usual velocity dependent factor when clocks move with respect to the isotropic reference frame S(0). In my oppinion the properties of the system S mentioned above are merely the consequence of the fact that a change in the clock synchronization procedure takes place and given that there are many synchronization procedures which are in accordance wirh Einstein's one, there are many S reference frames in which the transformation equations for space and time have a non=-standard shape? Your oppinion is highly appreciated. Thanks in advance. I have learned from somewhere that each problem has three answers: mine, yours and a third which is the correct one.