@article{AM2_1981__23_136890,
     author = {George M. Bergman},
     title = {Hyperidentities of groups and semigroups.},
     journal = {Aequationes mathematicae},
     pages = {50--65},
     publisher = {mathdoc},
     volume = {23},
     year = {1981},
     zbl = {0453.08003},
     url = {http://geodesic.mathdoc.fr/item/AM2_1981__23_136890/}
}