 part of a common facet.
        Both polyhedrons must be in H-representation. If they are not, the irredundant
        H-representation will be computed.
        
        The function tests if the intersection of two polyhedra <img src="../../../../../../fig/mpt/modules/geometry/sets/@Polyhedron/isneighbor3.png" alt="../../../../../../fig/mpt/modules/geometry/sets/@Polyhedron/isneighbor3.png"> and <img src="../../../../../../fig/mpt/modules/geometry/sets/@Polyhedron/isneighbor4.png" alt="../../../../../../