What is the relationship between Syriza and Alexis Tsipras 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.

While the result is a victory for Prime Minister Alexis Tsipras in that he managed to convince parliament to back him on the bailout, he did suffer a major rebellion from Syriza MPs for the second time in a week -- prompting analysts to predict he may be forced to call early elections.

Answer: chairperson