Não informado. (1977). Coal Abstracts. IEA Coal Research.
Lua i Stíl Chicago (17ú heag.)Não informado. Coal Abstracts. London: IEA Coal Research, 1977.
Lua MLA (8ú heag.)Não informado. Coal Abstracts. IEA Coal Research, 1977.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.