Woerkom, A. J. J. v. (1948). On the origin of comets.
Lua i Stíl Chicago (17ú heag.)Woerkom, Adrianus Jan Jasper van. On the Origin of Comets. 1948.
Lua MLA (8ú heag.)Woerkom, Adrianus Jan Jasper van. On the Origin of Comets. 1948.
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