Double taxation conventions : hearing before the Committee on Foreign Relations, United States Senate, Eighty-fifth Congress, second session, on Supplementary income tax protocol with the United Kingdom (Ex. A, 85th Cong., 2d sess.); Supplementary income tax convention with Belgium (Ex. B, 85th Cong., 2d sess.); and notification of extension of Income tax convention with the United Kingdom (Ex. C, 85th Cong., 2d sess.), July 1, 1958