A Lower Bound on the Self-intersections of Fold Singularities

TL;DR

This paper establishes sharp lower bounds on the number of self-intersections of fold singularities in smooth maps from surfaces to the plane, advancing understanding of surface singularity complexity.

Contribution

It introduces a novel lower bound for fold singularity self-intersections by linking boundary immersion properties to singular set analysis.

Findings

Sharp lower bound on self-intersections of boundary immersions.

Lower bound for self-intersections of fold singularities in stable maps.

Method connecting boundary component analysis to singular set complexity.

Abstract

For an oriented surface $S$, the singular set of a fold map $f:S\rightarrow \mathbb{R}^2$ is a collection of smooth curves, also known as fold singularities. We construct a sharp lower bound on the number of self-intersections of such fold singularities. This is done by first establishing a sharp lower bound on the number of self-intersections of the boundary of a surface immersed in $\mathbb{R}^2$. We then construct a sharp lower bound for the number of self-intersections of the singular set of a simple stable fold map of a surface to $\mathbb{R}^2$ by viewing the connected components of the singular set as the boundary components of smaller surface components, and invoking the previously constructed lower bound for the number of self-intersections of an immersed boundary.