@article{GDZPPN00239460X, title = {Free products of Hopf groups.}, journal = {Mathematische Zeitschrift}, volume = {85}, year = {1964}, pages = {274-284}, zbl = {0126.04803}, url = {http://dml.mathdoc.fr/item/GDZPPN00239460X} }
Dey, I.M.S. Free products of Hopf groups.. Mathematische Zeitschrift, Tome 85 (1964) pp. 274-284. http://gdmltest.u-ga.fr/item/GDZPPN00239460X/