TY - JOUR AU - Bethuel, F. TI - A characterization of maps in $H^1 (B^3, S^2)$ which can be approximated by smooth maps JO - Annales de l'I.H.P. Analyse non linéaire PY - 1990 SP - 269 EP - 286 VL - 7 IS - 4 PB - Gauthier-Villars UR - http://www.numdam.org/item/AIHPC_1990__7_4_269_0/ LA - en ID - AIHPC_1990__7_4_269_0 ER -