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@article{MZ_1990__205_3_174176, author = {Harry A.W.M. Kneppers}, title = {Two-dimensional formal groups: from isomorphism to isogeny.}, journal = {Mathematische Zeitschrift}, pages = {309--314}, publisher = {mathdoc}, volume = {205}, number = {3}, year = {1990}, zbl = {0685.14025}, url = {http://geodesic.mathdoc.fr/item/MZ_1990__205_3_174176/} }
Harry A.W.M. Kneppers. Two-dimensional formal groups: from isomorphism to isogeny.. Mathematische Zeitschrift, Tome 205 (1990) no. 3, pp. 309-314. http://geodesic.mathdoc.fr/item/MZ_1990__205_3_174176/