Kuiper, N. (1964) Contractibility of the Unitary Group in Hilbert Space. Topology, 3, 19-30.
https://doi.org/10.1016/0040-9383(65)90067-4

has been cited by the following article:

• TITLE: The Unitary Group in Its Strong Topology

  AUTHORS: Martin Schottenloher

  KEYWORDS: Unitary Operator, Strong Operator Topology, Topological Group, Infinite Dimensional Lie Group, Contractibility, Hilbert Bundle, Classifying Space

  JOURNAL NAME: Advances in Pure Mathematics, Vol.8 No.5, May 31, 2018

  ABSTRACT: The goal of this paper is to confirm that the unitary group U(H) on an infinite dimensional complex Hilbert space is a topological group in its strong topology, and to emphasize the importance of this property for applications in topology. In addition, it is shown that U(H) in its strong topology is metrizable and contractible if H is separable. As an application Hilbert bundles are classified by homotopy.