@article{MZ_1973__135_171996,
     author = {M.F. Newman and Jiri Sichler},
     title = {Free {Products} of {Hopf} {Groups.}},
     journal = {Mathematische Zeitschrift},
     pages = {69--72},
     publisher = {mathdoc},
     volume = {135},
     year = {1973},
     zbl = {0274.20040},
     url = {http://geodesic.mathdoc.fr/item/MZ_1973__135_171996/}
}