This definition is valid only for smooth surfaces without boundary mapped into three-space. The modern definition has a more algebraic flavor:

Note that this definition is valid for manifolds of arbitrary dimension, both smooth an polyhedral, with or without boundary, in spaces of any dimension.

**See also:**

- Tightness and its consequences

* 8/12/94 dpvc@geom.umn.edu -- *

*The Geometry Center*