@article{MZ_1968__105_170995,
     author = {Charles S. Ballantine},
     title = {On the {Hammard} {Product.}},
     journal = {Mathematische Zeitschrift},
     pages = {365--366},
     year = {1968},
     volume = {105},
     zbl = {0162.04204},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__105_170995/}
}