Section, Pub. L. 94–163, title I, § 102, Dec. 22, 1975, 89 Stat. 876; Pub. L. 94–385, title I, § 164, Aug. 14, 1976, 90 Stat. 1142; Pub. L. 95–619, title VI, § 691(b)(2), Nov. 9, 1978, 92 Stat. 3288; Pub. L. 95–620, title VIII, § 802, Nov. 9, 1978, 92 Stat. 3347, provided for incentives to develop underground coal mines.