Recently I was offered a PhD position at University X in Switzerland and I accepted it. I had been giving several interviews at several universities and this was the only decent offer I had in months, so I had no option but to accept it, and I liked it as well. Two weeks after accepting the offer and they having started the work visa process, I received a PhD offer from university Y (a much superior university and a great project), also in Switzerland! Now I plan to reject the PhD offer from university X, but the issue is its been three weeks since they started by process for work visa (I am an international candidate). Will my rejecting it at this stage affect my work visa situation at University Y? The offer I have from university Y is amazing and I really don't want to lose out on it because of legal issues. Can someone kindly advise me on it?