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

Prime Minister Alexis Tsipras resigned last week after his acceptance of an €86 billion rescue package for Greece's stricken economy triggered a major rebellion within his radical left Syriza party.
chairperson