TY - JOUR AU - Gorton, R. TI - $A$-systems JO - Compositio Mathematica PY - 1976 SP - 3 EP - 13 VL - 33 IS - 1 PB - Noordhoff International Publishing UR - http://archive.numdam.org/item/CM_1976__33_1_3_0/ LA - en ID - CM_1976__33_1_3_0 ER -