The function classes γ H (β,δ,d) and global linear Goursat problems
Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 24 (1970) no. 4, pp. 633-639. 
@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://www.numdam.org/item/ASNSP_1970_3_24_4_633_0/}
}
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Persson, Jan. The function classes $\gamma _H(\beta , \delta , d)$ and global linear Goursat problems. Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche, Série 3, Tome 24 (1970) no. 4, pp. 633-639. http://www.numdam.org/item/ASNSP_1970_3_24_4_633_0/

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