@article{1183534313, author = {Wang, Kai}, title = {Differentiable actions of $S^1$ and $S^3$ on homotopy spheres}, journal = {Bull. Amer. Math. Soc.}, volume = {79}, number = {5}, year = {1973}, pages = { 147-149}, language = {en}, url = {http://dml.mathdoc.fr/item/1183534313} }
Wang, Kai. Differentiable actions of $S^1$ and $S^3$ on homotopy spheres. Bull. Amer. Math. Soc., Tome 79 (1973) no. 5, pp. 147-149. http://gdmltest.u-ga.fr/item/1183534313/