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@article{CMH_1931__3_138548, author = {Arnold Emch}, title = {Ueber die {Abbildung} projektiver {R\"aume.}}, journal = {Commentarii mathematici Helvetici}, pages = {1--11}, publisher = {mathdoc}, volume = {3}, year = {1931}, zbl = {0001.29101}, url = {http://geodesic.mathdoc.fr/item/CMH_1931__3_138548/} }
Arnold Emch. Ueber die Abbildung projektiver Räume.. Commentarii mathematici Helvetici, Tome 3 (1931), pp. 1-11. http://geodesic.mathdoc.fr/item/CMH_1931__3_138548/