A four-sided Quadrilateral not contained in a plane. The problem of finding the minimum bounding surface of a
skew quadrilateral was solved by Schwarz (1890) in terms of Abelian Integrals and
has the shape of a Saddle. It is given by solving

**References**

Isenberg, C. *The Science of Soap Films and Soap Bubbles.* New York: Dover, p. 81, 1992.

Forsyth, A. R. *Calculus of Variations.* New York: Dover, p. 503, 1960.

Schwarz, H. A. *Gesammelte Mathematische Abhandlungen, 2nd ed.* New York: Chelsea.

© 1996-9

1999-05-26