BEIJING, May 13 (Xinhua) -- Chinese President Xi Jinping and Brazilian President Luiz Inacio Lula da Silva attended a signing ceremony of cooperation documents after holding talks in Beijing on Tuesday.Lula is on a state visit to China.At the Great Hall of the People, the two heads of state witnessed the signing of 20 cooperation documents covering the fields of development strategy alignment, science and technology, agriculture, digital economy, finance, inspection and quarantine, and media.