@article{ADM_2018_25_2_a5,
     author = {Iwona Krzy\.zanowska},
     title = {Cross-cap singularities counted with sign},
     journal = {Algebra and discrete mathematics},
     pages = {257--268},
     publisher = {mathdoc},
     volume = {25},
     number = {2},
     year = {2018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ADM_2018_25_2_a5/}
}