Alphabet Inc, the new holding company for Google, introduced its first share buyback and beat Wall Street’s profit forecast on Thursday, helped by solid progress in mobile and video advertising, sending the stock to its highest-ever level in after-hours trading. Revenue and profit well above analysts’ average forecasts, along with the unexpected buyback, was welcomed by Wall Street, which is now betting on further growth. At the same time, it is moving into a new corporate structure that will put more visibility on parts of Alphabet such as its secretive research arm, Google X.