@article{MS2_1975__37_166422,
     author = {Olof Heden},
     title = {A generalized {Lloyd} theorem and mixed perfect codes.},
     journal = {Mathematica Scandinavica},
     pages = {13--26},
     publisher = {mathdoc},
     volume = {37},
     year = {1975},
     zbl = {0318.94014},
     url = {http://geodesic.mathdoc.fr/item/MS2_1975__37_166422/}
}