Figure 5

Embedding the boundary of the orbit space. M is a 3-manifold with rotational symmetry. A is a symmetry cell, i.e., the image of the orbit space N under a cross-section κ. The boundary ∂N consists of parts E and S whose points correspond to the points in ∂M and in the axis of rotation, respectively. i _E and i _S are the inclusion maps of E and S into N, and κ _E embeds E into ∂M.