@incollection{AST_1985__S131__311_0,
     author = {Schmid, Wilfried},
     title = {Boundary value problems for group invariant differential equations},
     booktitle = {\'Elie Cartan et les math\'ematiques d'aujourd'hui - Lyon, 25-29 juin 1984},
     series = {Ast\'erisque},
     pages = {311--321},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {S131},
     year = {1985},
     mrnumber = {837206},
     zbl = {0621.22014},
     language = {en},
     url = {http://www.numdam.org/item/AST_1985__S131__311_0/}
}