@article{MAN_1996__304_4_165396,
     author = {Jaroslaw Wr\'oblewski},
     title = {A counterexample to the {L{\texttwosuperior}} estimate {//Xyu//...C(//X...u//} + {//Y...u//} + //u//).},
     journal = {Mathematische Annalen},
     pages = {93--98},
     publisher = {mathdoc},
     volume = {304},
     number = {4},
     year = {1996},
     zbl = {0835.47037},
     url = {http://geodesic.mathdoc.fr/item/MAN_1996__304_4_165396/}
}