Utilize the input text as a context reference, choose the right relationship between Alexis Tsipras and prime minister of Greece from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

ATHENS, Sept 21 Leftist leader Alexis Tsipras was sworn in as prime minister of Greece on Monday after sweeping to victory for a second term in parliamentary elections on Sunday.

Answer: position_held