fourbanger 1 2 3
e(1)+2*e(2)+3*e(3)
   fourbanger 0 1 2 3
e(2)+2*e(3)+3*e(4)
   fourbanger 1 0 3 4
e(1)+3*e(3)+4*e(4)
   fourbanger 0 0 0
0
   fourbanger 0
0
   fourbanger 1 1 1
e(1)+e(2)+e(3)
   fourbanger _1 _1 _1
-e(1)-e(2)-e(3)
   fourbanger _1 _2 0 _3
-e(1)-2*e(2)-3*e(4)
   fourbanger _1
-e(1)