Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: employer, creator, chief executive officer, chairperson

The latest news from Greece, where Prime Minister Alexis Tsipras contained a rebellion in his left-wing Syriza party to win a parliamentary vote, was seen as another positive for European markets.
chairperson