sentences:  In 1974, Hoan traveled to China for "medical treatment," but his real mission was probably related to the secret (and unsuccessful) Sino-Vietnamese border negotiations from August to November.He lost most of his influence after the Fourth National Party Congress in 1977, when the Vietnamese Communists shifted to a pro-Soviet position.Like Truong Nhu Tang, who went into exile in Paris, Hoang defected and surfaced in Beijing in July 1979, after shaking off political persecution by the Vietnamese communist authorities.