Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'Alexis Tsipras' from the options.
Options: owned by, chairperson, headquarters location, currency

Prime Minister Alexis Tsipras resigned last week after his acceptance of an 86 billion euro ($96 billion) rescue package for Greece's stricken economy triggered a major rebellion within his radical left Syriza party.
chairperson