@article{oprea_tanré_2005, 
  title={Flat circle bundles, pullbacks, and the circle made discrete}, 
  volume={2005}, 
  DOI={10.1155/ijmms.2005.3487}, 
  abstractNote={<jats:p>We use basic homotopical methods applied to Lie groups made discrete to prove that the real Euler class of a circle bundle vanishes if and only if the bundle is flat.</jats:p>}, 
  number={21}, 
  publisher={Hindawi Limited}, 
  author={Oprea and Tanré}, 
  year={2005}
  }