@article{MS2_1987__61_2_186096,
     author = {Marek Lassak and Andrzej Pr\'oszynski},
     title = {Algebraic and geometric approach to the classification of semispaces.},
     journal = {Mathematica Scandinavica},
     pages = {204--212},
     publisher = {mathdoc},
     volume = {61},
     number = {2},
     year = {1987},
     zbl = {0651.52002},
     url = {http://geodesic.mathdoc.fr/item/MS2_1987__61_2_186096/}
}