@article{PORMA_1985__43_1_114498,
     author = {Laffey, Thomas J.},
     title = {On a question of {Hills} concerning co-transposers},
     journal = {Portugaliae mathematica},
     pages = {179--187},
     publisher = {mathdoc},
     volume = {43},
     number = {1},
     year = {1985},
     mrnumber = {0875066},
     zbl = {0591.15006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1985__43_1_114498/}
}