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

Greek Prime Minister Alexis Tsipras is also under pressure from many in his radical left Syriza party who say the new accord will pile further austerity on a weakened economy and goes against the party's campaign pledges.
chairperson