Section, acts Aug. 16, 1954, ch. 736, 68A Stat. 211; July 6, 1960, Pub. L. 86–594, § 1, 74 Stat. 333; Sept. 12, 1966, Pub. L. 89–570, § 2(a), 80 Stat. 763; Dec. 30, 1969, Pub. L. 91–172, title V, § 504(a), 83 Stat. 632, related to pre-1970 exploration expenditures.