Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: member of, distributed by, chairperson, subsidiary

Greek Prime Minister Alexis Tsipras is trying to turn a corner after he reluctantly agreed to negotiate a third bailout, allowing the European Central Bank to top up bank credit lines but prompting a rebellion in his leftist Syriza party.
chairperson