@article{AM2_1980__20_182395,
     author = {Ronald P. Infante},
     title = {Strong normality and normality for difference fields.},
     journal = {Aequationes mathematicae},
     pages = {159--165},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0459.12018},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__20_182395/}
}