Underground coal operators install several new longwall mining systems: Several new names appear in the annual U.S. Longwall Census, but the population remains the same:52

• Autores: Steve Fiscor (ed. lit.)
• Localización: Coal age, ISSN 1091-0646, Vol. 113, Nº. 2, 2008, págs. 28-34
• Idioma: inglés
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