Surfaces36 of 113
Cross-cap
nineteenth-century topology
Another way to close a Möbius band with a disc: pinch it along a segment where the surface crosses itself. Like the Roman surface it is a picture of the projective plane, made here by mapping the sphere and folding it shut.
(x, y, z) ↦ (yz, 2xy, x² − y²)
On mathcurve.com as Bonnet croisé
Drawn as