In the context of the input sentence, determine the relationship between 'Syriza' and 'Alexis Tsipras'.
Options: chairperson, operator, platform, legal form

ATHENS (Reuters) - Rebels angered by Greece's international bailout walked out of the leftist Syriza party on Friday, formalising a widely-expected split after leader Alexis Tsipras resigned as prime minister to pave the way for early elections.
chairperson