1. Singularities of 2-spheres in 4-space and equivalence of knots;Fox;Bull. Am. Math. Soc.,1957
2. Piecewise linear isotopy and embedding of elements and spheres (I);Gugenheim;Proc. Lond. Math. Soc.,1953
3. Piecewise linear isotopy and embedding of elements and spheres (II);Gugenheim;Proc. Lond. Math. Soc.,1953
4. On regular neighbourhoods;Hudson;Proc. Lond. Math. Soc.,1964
5. On diffeomorphic approximations of polyhedral surfaces in 4-space;Kinoshita;Osaka Math. J.,1960