APA
"United Nations G. O. . E. C. F. E. S., "United Nations G. O. . E. C. F. E. S., . (1956). "International classification of hard, coals by type". Geneva: United Nations.
Chicago
"United Nations Government Of Economic Commission For Europe Secretariat", "United Nations Government Of Economic Commission For Europe Secretariat", . 1956. "International classification of hard, coals by type". Geneva: United Nations.
Harvard
"United Nations G. O. . E. C. F. E. S., "United Nations G. O. . E. C. F. E. S., . (1956). "International classification of hard, coals by type". Geneva: United Nations.
MLA
"United Nations Government Of Economic Commission For Europe Secretariat", "United Nations Government Of Economic Commission For Europe Secretariat", . "International classification of hard, coals by type". Geneva: United Nations. 1956.
