@article{MAN_1977__226_162948,
     author = {R.E. Stong},
     title = {Free  {S1} {Actions.}},
     journal = {Mathematische Annalen},
     pages = {151--154},
     year = {1977},
     volume = {226},
     url = {http://geodesic.mathdoc.fr/item/MAN_1977__226_162948/}
}