# .

# Whitney umbrella

In mathematics, specifically in the field of singularity theory, the Whitney umbrella (also referred to as Whitney's umbrella) is a self-intersecting rectangle placed in three dimensions.

It can be given by the parametric equations

(which is just the rectangle in 3-space.)

or by the implicit equation

x^{2} = y^{2}z

which also include the negative z axis (which is called the handle of the umbrella).

It is a local model of a pinch point singularity, together with the fold they are the only stable singularity of maps .

It is named after the American mathematician Hassler Whitney.

**See also
**

* cross-cap

**References
**

* Whitney's Umbrella. The Topological Zoo. The Geometry Center. Retrieved on 2006-03-08. (Images and movies of the Whitney umbrella.)

Undergraduate Texts in Mathematics