English

A new proof of Milnor-Wood inequality

Geometric Topology 2025-12-04 v5

Abstract

The Milnor-Wood inequality states that if a (topological) oriented circle bundle over an orientable surface of genus gg has a smooth transverse foliation, then the Euler class of the bundle satisfies E2g2.|\mathcal{E}|\leq 2g-2. We give a new proof of the inequality based on a (previously proven by the authors) local formula which computes E\mathcal{E} from the singularities of a quasisection. We also sketch two other proofs: one based on Poincar\`{e} rotation number theory, and the other of topological nature.

Keywords

Cite

@article{arxiv.2412.14553,
  title  = {A new proof of Milnor-Wood inequality},
  author = {Gaiane Panina and Timur Shamazov and Maksim Turevskii},
  journal= {arXiv preprint arXiv:2412.14553},
  year   = {2025}
}