Washington (AFP) – Put up your dukes, Vlad. Elon Musk, the world’s richest man, on Monday challenged Russian President Vladimir Putin to a fight, with nothing less than the fate of Ukraine, scene of Moscow’s brutal invasion, at stake. The eccentric billionaire and founder of aerospace company SpaceX took to Twitter, where his messages are notoriously erratic, to see whether the Russian leader would test his mettle in person rather than through his country’s forces. “I hereby challenge Vladimir Putin to single combat. Stakes are Ukraine,” said Musk. “Do you accept this fight?” he added in Russ…