@article{AIF_1998__48_3_667_0,
     author = {Schwarz, Gerry W. and Wehlau, David L.},
     title = {Invariants of four subspaces},
     journal = {Annales de l'Institut Fourier},
     pages = {667--697},
     publisher = {Association des Annales de l{\textquoteright}institut Fourier},
     volume = {48},
     number = {3},
     year = {1998},
     doi = {10.5802/aif.1634},
     mrnumber = {99i:14055},
     zbl = {0899.20024},
     language = {en},
     url = {http://archive.numdam.org/articles/10.5802/aif.1634/}
}