@article{CMH_1985__60_140000,
     author = {S.P. Plotnick and A. I. Suciu},
     title = {k-Invariants of knotted 2-spheres.},
     journal = {Commentarii mathematici Helvetici},
     pages = {54--84},
     publisher = {mathdoc},
     volume = {60},
     year = {1985},
     zbl = {0568.57017},
     url = {http://geodesic.mathdoc.fr/item/CMH_1985__60_140000/}
}