For ten points, identify this surface named for a German mathematician which has no interior or exterior.
The Etruscan Venus surface and the Ida surface are three-dimensional shad- ows of an embedding of this structure in four-dimensional space. Frederick Winsor's The Space Child's Mother Goose includes a rhyme about  three jolly sailors  who went to sea in one of these structures, however  the scenery seen was exceedingly dull / as the sea was entirely   inside the hull . This surface is the sole exception to the Heawood conjecture because its chromactic number is six, and it is nonorientable and has no boundary. This surface can be formed by adjoining two Möbius strips. For ten points, identify this surface named for a German mathematician which has no interior or exterior.
The Etruscan Venus surface and the Ida surface are three-dimensional shad- ows of an embedding of this structure in four-dimensional space.
Klein bottle