Utilize the input text as a context reference, choose the right relationship between Syriza and ATHENS from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

ATHENS (Reuters) - Greek Prime Minister Alexis Tsipras, struggling to contain a revolt in his left-wing Syriza party, said on Wednesday that his government would not implement reform measures beyond those agreed with lenders at a euro zone summit this month.

Answer: headquarters_location