United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "December 1986," PPI Detailed Report (December 1986) : 15-17. https://fraser.stlouisfed.org/title/63/item/21613/toc/276068 , accessed on April 25, 2024.
United States. Bureau of Labor Statistics. "Coal," in United States. Bureau of Labor Statistics. "December 1986," PPI Detailed Report (December 1986) : 15-17. https://fraser.stlouisfed.org/title/63/item/21613/toc/276068 , accessed on April 25, 2024.