The Whitney–Graustein theorem states that regular closed curves in the -plane are classified, up to regular homotopy, by their rotation number. Here we give a simple proof based on contact geometry.
Cite this article
Hansjörg Geiges, A contact geometric proof of the Whitney-Graustein theorem. Enseign. Math. 55 (2009), no. 1, pp. 93–102DOI 10.4171/LEM/55-1-4