defined by two opposing faces having the same number of vertices and
edges. These two faces should be connected by quadrangle "side" faces.
+\image html prism_mesh.png "Clipping view of a mesh of a prism with non-planar base and top faces"
+
The prism is allowed to have sides composed of several faces. (A prism
side is a row of faces (or one face) connecting the corresponding edges of
the top and base faces). However, a prism
