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@article{IM2_1976_10_4_a6, author = {I. M. Krichever}, title = {Obstructions to the existence of $S^1$-actions. {Bordism} of ramified coverings}, journal = {Izvestiya. Mathematics }, pages = {783--797}, publisher = {mathdoc}, volume = {10}, number = {4}, year = {1976}, language = {en}, url = {http://geodesic.mathdoc.fr/item/IM2_1976_10_4_a6/} }
I. M. Krichever. Obstructions to the existence of $S^1$-actions. Bordism of ramified coverings. Izvestiya. Mathematics , Tome 10 (1976) no. 4, pp. 783-797. http://geodesic.mathdoc.fr/item/IM2_1976_10_4_a6/