@article{MS2_1968__22_166049,
     author = {B. Jessen and J. Karpf and A. Thorup},
     title = {Some {Functional} {Equations} in {Groups} and {Rings.}},
     journal = {Mathematica Scandinavica},
     pages = {257--265},
     publisher = {mathdoc},
     volume = {22},
     year = {1968},
     zbl = {0183.04004},
     url = {http://geodesic.mathdoc.fr/item/MS2_1968__22_166049/}
}