1. Mapping a sphere into euclidian space;Babenko;Math. Notes,1990
2. Real value mappings of spheres;Floyd,1955
3. Verallgemeinerung bekanneter Abidungs—und Uberdeckugissat;Hopf;Portugal. Math.,1944
4. Problems in low dimensional topology;Kirby,1993
5. Problem 4;Knaster,1947