@article{MS2_1986__58_166971,
     author = {Johan P. Hansen and Simon Vydral},
     title = {Double points of compositions of projections.},
     journal = {Mathematica Scandinavica},
     pages = {119--124},
     publisher = {mathdoc},
     volume = {58},
     year = {1986},
     zbl = {0604.14008},
     url = {http://geodesic.mathdoc.fr/item/MS2_1986__58_166971/}
}