@article{MAN_1990__288_1_164727,
     author = {Xian Wu},
     title = {On an infinitesimal invariant of normal.},
     journal = {Mathematische Annalen},
     pages = {121--132},
     publisher = {mathdoc},
     volume = {288},
     number = {1},
     year = {1990},
     zbl = {0687.14006},
     url = {http://geodesic.mathdoc.fr/item/MAN_1990__288_1_164727/}
}