Roberts, J. (1992). The penguin history of the world. Penguin.
Lua i Stíl Chicago (17ú heag.)Roberts, J.M. The Penguin History of the World. 3rd.ed: Penguin, 1992.
Lua MLA (9ú heag.)Roberts, J.M. The Penguin History of the World. Penguin, 1992.
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