@article{AIHPC_1990__7_4_269_0, author = {Bethuel, F.}, title = {A characterization of maps in $H^1 (B^3, S^2)$ which can be approximated by smooth maps}, journal = {Annales de l'I.H.P. Analyse non lin\'eaire}, pages = {269--286}, publisher = {Gauthier-Villars}, volume = {7}, number = {4}, year = {1990}, mrnumber = {1067776}, zbl = {0708.58004}, language = {en}, url = {http://www.numdam.org/item/AIHPC_1990__7_4_269_0/} }