@article{ASNSP_1968_3_22_3_425_0,
     author = {Grubb, Gerd},
     title = {A characterization of the non local boundary value problems associated with an elliptic operator},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {425--513},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 22},
     number = {3},
     year = {1968},
     mrnumber = {239269},
     zbl = {0182.14501},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1968_3_22_3_425_0/}
}