@article{MS2_1976__39_166492,
     author = {Thomas J. Laffey},
     title = {Commutative subrings of periodic rings.},
     journal = {Mathematica Scandinavica},
     pages = {161--166},
     publisher = {mathdoc},
     volume = {39},
     year = {1976},
     zbl = {0344.16023},
     url = {http://geodesic.mathdoc.fr/item/MS2_1976__39_166492/}
}