@article{CMUC_1991__32_2_a4,
     author = {Fitzpatrick, Simon and Calvert, Bruce},
     title = {Sets invariant under projections onto  two dimensional subspaces},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {233--239},
     publisher = {mathdoc},
     volume = {32},
     number = {2},
     year = {1991},
     mrnumber = {1137784},
     zbl = {0756.46010},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1991__32_2_a4/}
}