%0 Journal Article %A Gorton, R. %T $A$-systems %J Compositio Mathematica %D 1976 %P 3-13 %V 33 %N 1 %I Noordhoff International Publishing %U http://archive.numdam.org/item/CM_1976__33_1_3_0/ %G en %F CM_1976__33_1_3_0