Ridge

In higher-dimensional geometry, the ridges are the (n-2)-subfacets of any n-polytope. A ridge is seen as the boundary between exactly two facets of a polytope or honeycomb. The ridges of a polytope should always be the contact region of two facets, otherwise it is an exotic polytope.

For example:

• The ridges of a 1D polytelon are null.
• The ridges of a 2D polygon or 1D tiling are its 0-faces or vertices.
• The ridges of a 3D polyhedron or plane tiling are its 1-faces or edges.
• The ridges of a 4D polychoron or 3-honeycomb are its 2-faces or simply faces.
• The ridges of a 5D polyteron or 4-honeycomb are its 3-faces or cells.