On surfaces and their contours (Q1178737)

The author makes a detailed study of curves in projective 2-space that can appear as apparent contours of projections of surfaces in \(RP(3)\). Only curves with generic singularities are considered. The first main theorem expresses the genus of the curve in terms of orientability, winding numbers and properties of the cusp points. The second main theorem shows how to compute the second Stiefel-Whitney class of any surface in \(RP(n)\) that projects into the curve in terms of the curve data and the set of singular elements of the intersection of the surfaces and a linear set of hyperplanes whose axis is an \((n-3)\)plane that does not meet the curve. The arguments are made clear by superb graphics.