What is the relationship between Alexis Tsipras and prime minister of Greece in the context of the input sentence. Choose an answer from: 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