@incollection{AST_1981__89-90__223_0,
     author = {Persson, J.},
     title = {Singular holomorphic solutions of linear partial differential equations with holomorphic coefficients and nonanalytic solutions of equations with analytic coefficients},
     booktitle = {Analytic solutions of partial differential equations - Trento, 1981},
     series = {Ast\'erisque},
     pages = {223--247},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {89-90},
     year = {1981},
     mrnumber = {666411},
     zbl = {0501.35018},
     language = {en},
     url = {http://archive.numdam.org/item/AST_1981__89-90__223_0/}
}