@article{ASNSP_1970_3_24_4_633_0,
     author = {Persson, Jan},
     title = {The function classes $\gamma _H(\beta , \delta , d)$ and global linear {Goursat} problems},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {633--639},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 24},
     number = {4},
     year = {1970},
     zbl = {0209.40102},
     language = {en},
     url = {http://archive.numdam.org/item/ASNSP_1970_3_24_4_633_0/}
}