@article{10_1090_S1079_6762_97_00038_3,
     author = {Higson, Nigel and Kasparov, Gennadi},
     title = {Operator {\dh}{\textthreequarters}-theory for groups which act properly and isometrically on {Hilbert} space},
     journal = {Electronic research announcements of the American Mathematical Society},
     pages = {131--142},
     publisher = {mathdoc},
     volume = {03},
     year = {1997},
     doi = {10.1090/S1079-6762-97-00038-3},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S1079-6762-97-00038-3/}
}