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 new law will come as a relief to Prime Minister Alexis Tsipras -- who is negotiating a new bailout worth up to 86 billion euros ($93 billion) over three years -- it saw him suffer a major rebellion amongst MPs in his leftist Syriza party for the second time in a week.

Answer: chairperson