@article{MAN_1989__284_4_164563,
     author = {K.Y. Lam and P.Y.H. Yiu},
     title = {Geometry of normed bilinear maps and the 16-square problem.},
     journal = {Mathematische Annalen},
     pages = {437--448},
     publisher = {mathdoc},
     volume = {284},
     number = {4},
     year = {1989},
     zbl = {0649.10015},
     url = {http://geodesic.mathdoc.fr/item/MAN_1989__284_4_164563/}
}