ATHENS (Reuters) – Greek leftist leader Alexis Tsipras was sworn in as prime minister on Monday, a day after his sweeping election victory, in a brief and sober ceremony at the office of President Karolos Papoulias. Taking the oath without the traditional religious blessings that normally accompany the swearing in of a new prime minister and without a tie, Tsipras pledged to uphold the constitution after he had assured Papoulias that he had enough support to form a government. …