Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: chairperson, parent organization, operator, product/material produced

ATHENS, July 23 Greek Prime Minister Alexis Tsipras faced down a revolt by rebels in his leftists Syriza party to win parliament's backing on Thursday for a second package of reforms required to start talks on a financial rescue deal.
chairperson