@incollection{AST_1985__S131__9_0,
     author = {Berger, Marcel},
     title = {La g\'eom\'etrie m\'etrique des vari\'et\'es riemanniennes (variations sur la formule $a^2 = b^2 + c^2 - 2bc \cos \alpha)$},
     booktitle = {\'Elie Cartan et les math\'ematiques d'aujourd'hui - Lyon, 25-29 juin 1984},
     series = {Ast\'erisque},
     pages = {9--66},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {S131},
     year = {1985},
     mrnumber = {837193},
     zbl = {0615.53028},
     language = {fr},
     url = {http://archive.numdam.org/item/AST_1985__S131__9_0/}
}