  In the last two decades, theories explaining the same experiments as well as
special relativity does, were developed by using different synchronization
procedures. All of them are ether-like theories. Most authors believe these
theories to be equivalent to special relativity, but no general proof was ever
brought. By means of a Gedankenexperiment on light aberration, we produce
strong evidence that this is the case for experiments made in inertial systems.
