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

ATHENS (Reuters) - The leftist Syriza party of former Prime Minister Alexis Tsipras will challenge Greece's creditors on unresolved aspects of the nation's bailout but implement unpopular reforms it has already agreed, it said on Sunday.
chairperson