Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: parent organization, chairperson, product/material produced, operator

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