@article{JRAM_1987__377_152923,
     author = {Nicholas M. Katz},
     title = {On a certain class of exponential sums.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {12--17},
     publisher = {mathdoc},
     volume = {377},
     year = {1987},
     zbl = {0604.12015},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1987__377_152923/}
}