A look at the rivalry between Kalshi CEO Tarek Mansour and Polymarket CEO Shayne Coplan, who have competing visions for how prediction markets should grow (Bobby Allyn/NPR)

Bobby Allyn / NPR: A look at the rivalry between Kalshi CEO Tarek Mansour and Polymarket CEO Shayne Coplan, who have competing visions for how prediction markets should grow   —  There's one word Kalshi CEO Tarek Mansour is loath to say: Polymarket.  —  Like a politician swiping his never-to-be-spoken …