Abstract
We give short proofs of the following two facts: Iterated principal circle bundles are precisely the nilmanifolds. Every iterated circle bundle is almost flat, and hence diffeomorphic to an infranilmanifold.
Citation
Igor Belegradek. "Iterated circle bundles and infranilmanifolds." Osaka J. Math. 57 (1) 165 - 168, January 2020.