@article{AM2_1993__46_2-3_137536,
     author = {J\"urg R\"atz and Karl Baron},
     title = {Orthogonal and additivity modulo a subgroup.},
     journal = {Aequationes mathematicae},
     pages = {11--18},
     year = {1993},
     volume = {46},
     number = {2-3},
     zbl = {0789.39004},
     url = {http://geodesic.mathdoc.fr/item/AM2_1993__46_2-3_137536/}
}