@article{10_14708_cm_v18i2_5820,
     author = {Th. Friedrich},
     title = {On an equality for 3-dimensional manifolds},
     journal = {Commentationes Mathematicae},
     pages = { 187--188},
     year = {1975},
     volume = {18},
     number = {2},
     doi = {10.14708/cm.v18i2.5820},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/articles/10.14708/cm.v18i2.5820/}
}