@article{10_4153_CMB_1967_055_3,
     author = {Williams, Kenneth S.},
     title = {On {A} {Theorem} of {Niven}},
     journal = {Canadian mathematical bulletin},
     pages = {573--578},
     year = {1967},
     volume = {10},
     number = {4},
     doi = {10.4153/CMB-1967-055-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1967-055-3/}
}