@article{700779,
     title = {\"Uber 2-Banach-Ra\"ume},
     booktitle = {General Topology and its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1972},
     pages = {143-144},
     mrnumber = {MR0259566},
     zbl = {0307.46016},
     url = {http://dml.mathdoc.fr/item/700779}
}

Gähler, S. Über 2-Banach-Raüme, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1972), pp. 143-144. http://gdmltest.u-ga.fr/item/700779/