@article{IM2_1981_16_3_a3,
     author = {G. G. Kasparov},
     title = {The operator $K$-functor and extensions of $C^*$-algebras},
     journal = {Izvestiya. Mathematics },
     pages = {513--572},
     publisher = {mathdoc},
     volume = {16},
     number = {3},
     year = {1981},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1981_16_3_a3/}
}