For legal reasons, the thesis supervisor has to be a professor in most unis (a non supervising advisor can be anyone with a doctorate, though), not just a random postdoc fellow.
> For legal reasons, the thesis supervisor has to be a professor in most unis
you're wrong - eg in my uni (a "top tier" uni) thesis advisor could be a RAP (research associate professor) which was not a full nor tenure track prof and thus not much more than a postdoc.
you're wrong - eg in my uni (a "top tier" uni) thesis advisor could be a RAP (research associate professor) which was not a full nor tenure track prof and thus not much more than a postdoc.