@article{MZ_1993__214_1_174557,
     author = {Graham Ellis},
     title = {Crossed squares and combinatorical homotopy.},
     journal = {Mathematische Zeitschrift},
     pages = {93--110},
     publisher = {mathdoc},
     volume = {214},
     number = {1},
     year = {1993},
     zbl = {0789.55008},
     url = {http://geodesic.mathdoc.fr/item/MZ_1993__214_1_174557/}
}