1. Further Pure Mathematics;Bostock,1982
2. On k-to-1 transformations;Gottschalk;Bull. Amer. Math. Soc.,1947
3. The non-existence of a certain type of continuous transformations;Harrold;Duke Math. J.,1939
4. Every exactly 2-to-1 function on the reals has an infinite set of discontinuities;Heath;Proc. Amer. Math. Soc.,1986
5. k-to-1 functions between graphs with finitely many discontinuities;Heath;Proc. Amer. Math. Soc.,1988