[B2] T.F. Banchoff, Triple points and singularities of
projections of smoothly immersed surfaces,
Proc. Amer. Math. Soc. 46 (1974) 402-406.
The author proves that the number of triple points in an immersion of
a smooth surface is congruent modulo 2 to the Euler characteristic of
the surface, and that the homology class of the double set of an
immersion is a topological invariant. He gives a geometric
interpretation of Whitney duality.
Bibliography
10/12/94 dpvc@geom.umn.edu --
The Geometry Center