@incollection{SB_2002-2003__45__321_0, author = {Connes, Alain}, title = {Nombres de {Betti} $L^2$ et facteurs de type ${\rm II}_1$}, booktitle = {S\'eminaire Bourbaki : volume 2002/2003, expos\'es 909-923}, author = {Collectif}, series = {Ast\'erisque}, note = {talk:920}, pages = {321--333}, publisher = {Association des amis de Nicolas Bourbaki, Soci\'et\'e math\'ematique de France}, address = {Paris}, number = {294}, year = {2004}, zbl = {1133.46032}, language = {fr}, url = {http://archive.numdam.org/item/SB_2002-2003__45__321_0/} }