@article{IM2_1970_4_1_a1,
     author = {A. A. Karatsuba},
     title = {Estimates of character sums},
     journal = {Izvestiya. Mathematics },
     pages = {19--29},
     publisher = {mathdoc},
     volume = {4},
     number = {1},
     year = {1970},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1970_4_1_a1/}
}