What is the relationship between 'Syriza' and 'Alexis Tsipras' in the context of the input sentence.
Options: owner of, business division, position held, chairperson

1236 - Greek Prime Minister Alexis Tsipras appeals to his leftist Syriza party's lawmakers to back a tough reforms package after abruptly offering last-minute concessions to try to save the country from financial meltdown.
chairperson