@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/}
}