@article{BUMI_2000_8_3B_1_a6,
     author = {Tzvetkov, Nickolay},
     title = {Remark on the null-condition for the nonlinear wave equation},
     journal = {Bollettino della Unione matematica italiana},
     pages = {135--145},
     publisher = {mathdoc},
     volume = {Ser. 8, 3B},
     number = {1},
     year = {2000},
     zbl = {0949.35090},
     mrnumber = {654209},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/BUMI_2000_8_3B_1_a6/}
}