whose intersection is also homeomorphic to Related spaces More examples of open, contractible 3-manifolds may be constructed by proceeding in similar fashion and picking different embeddings of in in the iterative process. Each embedding should be an unknotted solid torus in the 3-sphere. The essential properties are that the meridian of should be null-homotopic in the complement of and in addition the longitude of should not be null-homotopic in Another variation is to pick several subtori at each stage instead of just one. The cones over some of these continua appear as the complements of Casson handles in a 4-ball. The dogbone space is not a manifold but its product with is homeomorphic to See also List of topologies Tame manifold References Further reading 3-manifolds Differential geometry Geometric topology Manifolds