The side approximation
theorem proved by R. H. Bing and later improved by F. M. Lister states
that a sphere S topologically embedded in Euclidean three space can be 𝜖−
approximated with polyhedral spheres g(S) and h(S) such that g(S −∪Gi) ⊂ Int
S,g(Gi) ∩ S ⊂ Gi,h(S −∪Hi) ⊂ExtS, and h(Hi) ∩ S ⊂ Hi where {Gi} and {Hi}
are respectively finite collections of disjoint 𝜖-disks in S. In this article the theorem is
strengthened by showing that the sets ∪Gi and ∪Hi may also be taken to be
disjoint.