Winding numbers and Fourier series

Abstract

This is an expository talk on a topic of classical analysis, arising from the VMO theory of the topological degree due to Br\'ezis and Nirenberg (1995). We sketch the history of the subject and some of its recent developments. The paper is organized as a sequence of questions. Most of them, in particular the last one, deal with Fourier series of continuous functions of constant absolute value. One of them contains new results on the comparison of summation processes.