%0 Journal Article %A Bethuel, F. %T A characterization of maps in $H^1 (B^3, S^2)$ which can be approximated by smooth maps %J Annales de l'I.H.P. Analyse non linéaire %D 1990 %P 269-286 %V 7 %N 4 %I Gauthier-Villars %U http://www.numdam.org/item/AIHPC_1990__7_4_269_0/ %G en %F AIHPC_1990__7_4_269_0