@article{ASENS_1972_4_5_2_183_0,
     author = {Burghelea, Dan},
     title = {Free differentiable $S^1$ and $S^3$ actions on homotopy spheres},
     journal = {Annales scientifiques de l'\'Ecole Normale Sup\'erieure},
     pages = {183--215},
     publisher = {Elsevier},
     volume = {Ser. 4, 5},
     number = {2},
     year = {1972},
     doi = {10.24033/asens.1224},
     mrnumber = {46 #6380},
     zbl = {0247.57009},
     language = {en},
     url = {http://www.numdam.org/articles/10.24033/asens.1224/}
}