Answer: Cierto.
The statement "El Mercado de Guadalupe está abierto cada martes" is a statement in Spanish that translates to "The Guadalupe Market is open every Tuesday" in English. This statement is true, as it indicates that the market is open on Tuesdays, and does not make any claims about the market being open on any other days. Therefore, the statement is true, or "cierto" in Spanish.