Guitart, R. (1979). Carrés exacts. Math. Forschunginstitut Oberwolfach, 42–44. 
@article{guitart1977carres,
  title = {Carrés exacts},
  author = {Guitart, René},
  year = {1979},
  month = aug,
  journal = {Math. Forschunginstitut Oberwolfach},
  pages = {42--44}
}