@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/} }