Wolff Douglas, D. (1925). Guillaume De Greef: The social theory of an early syndicalist. New York: Columbia University.
Lua i Stíl Chicago (17ú heag.)Wolff Douglas, Dorothy. Guillaume De Greef: The Social Theory of an Early Syndicalist. New York: Columbia University, 1925.
Lua MLA (8ú heag.)Wolff Douglas, Dorothy. Guillaume De Greef: The Social Theory of an Early Syndicalist. New York: Columbia University, 1925.
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