@article{MZ_1993__214_1_174551,
     author = {M.S. Ravi},
     title = {An effective version of {Nor's} theorem.},
     journal = {Mathematische Zeitschrift},
     pages = {1--8},
     publisher = {mathdoc},
     volume = {214},
     number = {1},
     year = {1993},
     url = {http://geodesic.mathdoc.fr/item/MZ_1993__214_1_174551/}
}